Replaying a single-diagram kifu is closer in feel to an actual game. At least one is forced to look around inside the record for each move. This trains the brain to look at the board and read out moves before putting down a stone, I think. Also, less paper is used
The 50-move-diagram kifu are easier to play through and may be more digestible for beginners who find single diagrams too time-consuming. This might be better for replaying just to absorb moves.