Me personally, I would never trim upper leaves. Really, the right answer to whether to trim them or not, a light meter would help. For example: in my closet with 2 1000 watters running, I can go below the canopy with my light meter, in many cases, the meter is fully pegged. So if I trimmed leaves off, I would get less of a yield. It all depends on the amount of light, type of light, and strain.