There is a raging debate over this question and with no clear winner as far as I can see. My short answer is I have no idea but here are some things to consider....

I think the argument goes like this - the more fan leaves means the more light can be absorbed by the plant so the bud sites will benefit from more fan leaves. This argument is bolstered by the "never prune during flowering mantra".

The other argument is plants use valuable energy on maintenance and nutrition for fan leaves that would be better spent on buds. This argument gets a lift when you consider that there are leaves right in the buds that can do the job of the fan leaves.

Like most things, maybe a mix of the two (lightly pruning but leaving plenty of fan leaves on the plant) is the right way to go? That's what i do but i have no clue as to whether this is correct or not.