I'm going to catch flak, and I really don't care, but pruning is acceptable in the plant world. It is done for a number of reasons. I can't wait for someone to tell me this works on all plants BUT marijuana, LOL...
Anyways, pruning of suckers, diseased or weak areas, lower branches is ideal to promote vigourous new growth at the top of the plant. Pruning can also be used to shape a plant and as many know, it can be used to increase the number of colas through a pruning method known as topping or fimming. It also improves circulation around plants and helps prevent mold and mildew in cramped grow spaces.
You are going to read a lot of advice on here that blasts anyone who would dare cut off a fan leaf or prune their plants. I say ignore them and do what you think is right for your plants. I would not recommend pruning during flowering, as the shock caused may delay harvest up to a month. The only exception is to remove near dead material (yellow). Experiment and learn. Keep an eye on plants that you prune and watch the results. If you have a camera, record before and after shots and share them. Sooner or later, we'll break up some myths going around.