Even Jorge Cervantes will tell you to trim leaves, IF your canopy is too thick (I would say he is more experienced than most on RIU.) Obviously fan leaves absorb light, to photosynthesize- but they also block light from anything in their shadow (as do all physical materials.) The fan leaves only die during flower because the plant is using the energy stored in them, ONLY because when you are flowering (if you know what you're doing), you are giving the plant less nitrogen and more phosphorous and potassium... this is the best way to feed for the biggest/best flower production, so DON'T add any nitrogen (of course.) Point being- they aren't shedding their leafs because they don't need them anymore. It's true that photosynthesis occurs in the leaves but it also occurs in the buds themselves (as well as the rest of the plant other than roots.) That, my friends, is the only reason cannabis appears green in the first place... beneath the green color of chlorophyll, ALL cannabis plants are violet in color. What I'm getting at is fan leaf trimming is a technique used by seasoned professional growers, but only when it's absolutely necessary.
If you remove all leafs, you will see bud production slow to a halt. If you experiment and strategically remove SOME fan leafs you will see advantages & disadvantages to both sides, then you will learn when/WHERE to do it... and when to refrain. Because it CAN be beneficial, but it can hurt you as well.
P.s.- if a fan leaf is yellowing, IMO, it's best to let it fall off on it's own as the plant is currently feeding off of it if it is already yellowed.