From what I understand/recall, it has been found to generally improve move selection (higher rating in internal tests with the setting enabled)
I wouldn't think of it as something to optimize and would leave it on unless someone gives a good reason as to why not.
Edit:
https://github.com/leela-zero/leela-zero/issues/2411 - here is discussion from 2019 about it and whether or not its good to enable in training games. A quote from the first post (by lightvector) is
"So it seems like at least in KataGo, LCB seems not to be a clear benefit for training, and if anything, LCBMoves perhaps makes it worse. This is despite the fact that I've already verified with the same versions of KataGo that LCB easily adds +100 Elo or more at similar numbers of visits!"
Where we see that the parameter appears to be very beneficial in terms of playing strength, but may not be ideal for producing training games