I trim the really thick plants like Purple Kush and Gods Gift to let air and sun in to prevent mold. The buds are so thick they will just mold from the dew at night otherwise. The Pineapple has thin airy leaves so I don't trim any leaves unless they are already dying. With Sour Diesel I just trim a few of the leaves to let light and air in. I trim the popcorn buds only near harvest when I am sure they won't get any bigger.

I finish all my plants outdoors so the info on whether to trim indoors may be different.