Invading the corner

[Uberdude]

Black can make a wall with , which threatens to kill the white stone, so white replies with . Black is showing a net profit here already. Next he can hane, which forces white down one row, making black's net profit about 1.5 to 2 points per stone. White makes a slight change of direction to ensure eye space with 4 thru 7, then continues with 8, 9, and 10, and black finishes with 'a'. ( This is the simplest variation. There are more complex variations, but let's stick to the natural play for the sake of example. )

$$Bc
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$$ | . . 7 . . . . . . . . .
$$ | . 5 . . . . . . . . . .
$$ | . 4 1 X b . . . . , . .
$$ | . 6 W 2 3 9 a . . . . .
$$ | . . . . 8 0 . . . . . .
$$ | . . . . . . . . . . . .
$$ ----------------------------

Click Here To Show Diagram Code

[go]$$Bc
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$$ | . . 7 . . . . . . . . .
$$ | . 5 . . . . . . . . . .
$$ | . 4 1 X b . . . . , . .
$$ | . 6 W 2 3 9 a . . . . .
$$ | . . . . 8 0 . . . . . .
$$ | . . . . . . . . . . . .
$$ ----------------------------[/go]

This is a huge mistake for white, and shows the dangers of blindly memorizing the end position of josekis rather than thinking about your moves as you play them. 4 should be played at 8. Playing at 4 immediately is a big mistake in order as black should not make the hanging connection at 7 but rather solid connect at b. Then white can only make a sealed in L+2 group in gote (but with a clamp aji on 5) which is far inferior to the joseki result of a non-sealed in group in sente.

$$Bc
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$$ | . . . X . . . . . , . .
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$$ | . . X . . . . . . . . .
$$ | . X . . . . . b . . . .
$$ | . O X X . . . . . X . .
$$ | . O O O X X X . . . . .
$$ | . . . . O O . . . . . .
$$ | . . . . . . . . . . . .
$$ ----------------------------

Click Here To Show Diagram Code

[go]$$Bc
$$ | . . . . . . . . . . . .
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$$ | . . . X . . . . . , . .
$$ | . . . . a . . . . . . .
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$$ | . . X . . . . . . . . .
$$ | . X . . . . . b . . . .
$$ | . O X X . . . . . X . .
$$ | . O O O X X X . . . . .
$$ | . . . . O O . . . . . .
$$ | . . . . . . . . . . . .
$$ ----------------------------[/go]

...and there are still invasions or reductions of the sides with moves like 'a' or 'b'.

Err, what? 'a' or 'b' both look fairly unlikely to be good moves and far too close to black's strong group, likely creating heavy groups. Usually you just give black that territory and try to make him depressed from being overconcentrated.

Again, the benefits of an invasion are apparent when contrasted with a diagram in which black gets the 3-3 first:

$$Bc
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$$ | . . . X . . . . . , . .
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$$ | . . . c . . . . . . . .
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$$ | . . . X . . . . . X . .
$$ | . . X . . . b . . . . .
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$$ | . . . . . . . . . . . .
$$ ----------------------------

Click Here To Show Diagram Code

[go]$$Bc
$$ | . . . . . . . . . . . .
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$$ | . . . X . . . . . , . .
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$$ | . . . c . . . . . . . .
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$$ | . . . X . . . . . X . .
$$ | . . X . . . b . . . . .
$$ | . . . . . . . . . . . .
$$ | . . . . . . . . . . . .
$$ ----------------------------[/go]

Now the corner is out of reach, and even the side invasions can be attacked vigorously.

Adding a move at 3-3 is one possiblity, but more normal would be to add a one point jump at a (and which side you pick depends on the rest of the board).

P.S. I call it an invasion, as do many others (including pros).

[EdLee]

which beginners often miss - is that the 4-4 stone has 0% of the corner.

This depends entirely on how you define "the corner". In the opening, we usually consider "taking an empty corner"
to include various moves like 3-4, 3-3, 3-5, 4-5, and 4-4.

I would say the 4-4 has SOME prescence in the corner.

PS. I agree many beginners (including myself) at first would misunderstand the 4-4
to mean owning a significant chunk of the corner.

[EdLee]

P.S. I call it an invasion, as do many others (including pros).

Actually, this is an interesting point. In Chinese and Japanese, I'm not sure they use "invade" for the above 3-3 placements, do they?
(No idea about in Korean... Kirby?)

[oren]

In　Japanese, it's 打ち込み, uchikomi. While it's not directly invade, I think "invade" is ok to use. "Playing inside" would be more literal.

[Shaddy]

In chinese, the verb used with the 3-3 invasion is dian3, which I don't think translates to 'invade'

[speedchase]

Joaz, if the 4,4 actually had zero presence in the corner, then playing the 3,3 would be an equal result

[illluck]

In chinese, the verb used with the 3-3 invasion is dian3, which I don't think translates to 'invade'

That's one way to say it, though dian as a term in Go actually implies that it's a move inside. Another (less commonly used) term is just 3-3 入侵 (invasion).

[bleep]

Many thanks to those who took what looks to be a lot of time for the diagrams! Now to internalise that...!

[countsheep]

In most cases, when the two wings are the same length. 33 invasion would be a good choice. It's not about "early" or "late".
It as simply as, if a=b, go 33.

$$Bc
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$$ | . . . . . . . . . . . . . . . . b . . |
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$$ | . . . , . . . . . , . . . . . , X . . |
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$$ ---------------------------------------
$$ {AR R15 R10}
$$ {AR P17 K17}
$$ {AR P17 Q17}
$$ {AR R15 R16}

Click Here To Show Diagram Code

[go]$$Bc
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$$ | . . . . . . . . . X . . a . . . W . . |
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$$ | . . . . . . . . . . . . . . . . b . . |
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$$ | . . . , . . . . . , . . . . . , X . . |
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$$ ---------------------------------------
$$ {AR R15 R10}
$$ {AR P17 K17}
$$ {AR P17 Q17}
$$ {AR R15 R16}[/go]

It's easy to understand. When you invade 33, the opponent has to choose between a and b. If you didn't have a stone at c, of course the opponent would block a. It's too easy for the opponent to make a choice, and after the joseki, b's efficiency is high.

$$Bc
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$$ | . . . . . . . . . X . . . . . a W . . |
$$ | . . . , . . . . . , . . . . . X b . . |
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Click Here To Show Diagram Code

[go]$$Bc
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$$ | . . . . . . . . . X . . . . . a W . . |
$$ | . . . , . . . . . , . . . . . X b . . |
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$$ ---------------------------------------[/go]

If the wings are not the same length, 33 is not a good choice. Black will definitely block b for a higher efficiency. Apparently, the right side is bigger.

$$Bc
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$$ | . . . . . . . . . X . . . . . a W . . |
$$ | . . . , . . . . . , . . . . . X b . . |
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$$ ---------------------------------------

Click Here To Show Diagram Code

[go]$$Bc
$$ ---------------------------------------
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$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . X . . . . . a W . . |
$$ | . . . , . . . . . , . . . . . X b . . |
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$$ ---------------------------------------[/go]

In this diagram, the two wings are the same length. The opponent would be hard to make a choice. And, if the opponent blocks a(if block b, the result is the same),

$$Bc
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$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . X . . . . . a W . . |
$$ | . . . , . . . . . , . . . . . X b . . |
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$$ | . . . , . . . . . , . . . . . , X . . |
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$$ ---------------------------------------

Click Here To Show Diagram Code

[go]$$Bc
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . X . . . . . a W . . |
$$ | . . . , . . . . . , . . . . . X b . . |
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$$ | . . . , . . . . . , . . . . . , X . . |
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$$ ---------------------------------------[/go]

The circle marked stone is not efficient. That's an evidence why white's 33 invasion was a good choice. With an influence like this, black's two space extension is really slow. Black should extend further, or play somewhere else.

$$Bc
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . X O O . . |
$$ | . . . . . . . . . X . . . X . X O . . |
$$ | . . . , . . . . . , . . . . . X O . . |
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$$ | . . . , . . . . . , . . . . . , B . . |
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$$ ---------------------------------------

Click Here To Show Diagram Code

[go]$$Bc
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . X O O . . |
$$ | . . . . . . . . . X . . . X . X O . . |
$$ | . . . , . . . . . , . . . . . X O . . |
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$$ | . . . , . . . . . , . . . . . , B . . |
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$$ ---------------------------------------[/go]

That's it.

Here are two videos to learn corner techniques.
http://www.gocommentary.com/free-videos ... art-1.html
http://www.gocommentary.com/free-videos ... art-1.html

[hyperpape]

Interesting perspective. But what about

$$Bc
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Click Here To Show Diagram Code

[go]$$Bc
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$$ | . . . , . . . . . , . . . . . , . . . |
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$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]

or

$$Bc
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . W . . |
$$ | . . . , . . . . X , . . . . . X . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . X . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------

Click Here To Show Diagram Code

[go]$$Bc
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . W . . |
$$ | . . . , . . . . X , . . . . . X . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . X . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
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$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]

[bleep]

So because you are forcing an inefficiency, that makes it a worthwhile play? It seems to me that this would only really start to affect your game at a much higher level than kyu level? Obviously, all the small inefficiencies will add up and result in a generally poorer standard of play, but don't you need to be able to take advantage of these inefficiencies in order to benefit? I wouldn't have a clue how to benefit from the diagram below!

Musing further, I suppose the benefit of the below is passive, in that you have 'wasted' a move of the opponents'?

...

The circle marked stone is not efficient. That's an evidence why white's 33 invasion was a good choice. With an influence like this, black's two space extension is really slow. Black should extend further, or play somewhere else.

$$Bc
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . X O O . . |
$$ | . . . . . . . . . X . . . X . X O . . |
$$ | . . . , . . . . . , . . . . . X O . . |
$$ | . . . . . . . . . . . . . . . . X O . |
$$ | . . . . . . . . . . . . . . . . X O . |
$$ | . . . . . . . . . . . . . . . . X . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , B . . |
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$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------

Click Here To Show Diagram Code

[go]$$Bc
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . X O O . . |
$$ | . . . . . . . . . X . . . X . X O . . |
$$ | . . . , . . . . . , . . . . . X O . . |
$$ | . . . . . . . . . . . . . . . . X O . |
$$ | . . . . . . . . . . . . . . . . X O . |
$$ | . . . . . . . . . . . . . . . . X . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , B . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]

That's it.

Here are two videos to learn corner techniques.
http://www.gocommentary.com/free-videos ... art-1.html
http://www.gocommentary.com/free-videos ... art-1.html

[countsheep]

Interesting perspective. But what about

In your diagrams, invading san-san is a good choice.

For the same reason, in the diagram below, invading 33 would be not good.

$$Bc
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . W . . |
$$ | . . . , . . . . . X . . . . . X . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . X . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------

Click Here To Show Diagram Code

[go]$$Bc
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . W . . |
$$ | . . . , . . . . . X . . . . . X . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . X . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]

The rule is applicable if the wing stone is on the point a-j.
Of course, we are talking about local. Sometimes we should think of the whole board.

$$Bc
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . a c e g i . . . W . . |
$$ | . . . , . . . . b d f h j . . X . . . |
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$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------

Click Here To Show Diagram Code

[go]$$Bc
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . a c e g i . . . W . . |
$$ | . . . , . . . . b d f h j . . X . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]

[Alguien]

So because you are forcing an inefficiency, that makes it a worthwhile play? It seems to me that this would only really start to affect your game at a much higher level than kyu level?

That (common) reasoning doesn't work in go. It's equivalent to playing for territory because influence is harder.

Go works on a system of equilibriums, if you bias one side for any reason other than the position on the board, you're forcing yourself to play worse than what's possible for you.

You may argue that it's worse in a way that will make it easier for you to win that game. But at the same time, that behaviour is self-feeding: you need to play for territory to win because you play worse because you play for territory to win even while knowing it's not the best move.

Forcing an inefficiency is objectively good. If it doesn't give you an advantage you can either change that fact and advance or not force the inefficiency and enter the self feeding loop.

[Phelan]

So because you are forcing an inefficiency, that makes it a worthwhile play?

I think that is partly it, but also that you get to play there before the opponent. If you let him play there, the corner gets settled, and becomes huge.

In the cases where the distance is not the same, however, there is usually a better invasion/reduction than just playing 3-3.
At least, that's what I think people were meaning.

[Uberdude]

Obviously, all the small inefficiencies will add up and result in a generally poorer standard of play, but don't you need to be able to take advantage of these inefficiencies in order to benefit? I wouldn't have a clue how to benefit from the diagram below!

Musing further, I suppose the benefit of the below is passive, in that you have 'wasted' a move of the opponents'?

Right, the inefficiency is already a good result for you. They aren't something you need to find a follow-up for to take advantage, you already have one. The way this is manifest is by counting at the end of the game. As you both played the same number of moves (assuming you don't bizarrely start passing in the middle of the game) then if your stones are more efficient then you will have more territory and win.