I would say don't ever cut the fan leaves off unless you need to keep them smaller for some reason. Those are the food factories of your plant. If you are worried about the lower plant not being able to get enough sunlight, then just cut off the branches at the bottom two or three nodes, so that the focus of the plants energy is the well-lit top. I don't know if i would do this if the plant is already flowering. You probably want a little veg time after the cut, so the plant can fully recover. If you want good weed then you need a healthy plant. If you do need to trim just don't over-do it.