Fan leaves that are toward the center of the plant, that aren't getting much light themselves anyway, find their way into my compost pile. I take a bottom-up, inside-out approach, and apply the concepts of Medjool farming, where I select out the sites that have the least potential based on amount of light and other physical location factors. This is when I usually take clones, and that's once I see that buds are beginning to set well, which makes it easy for me to say, "Oh yeah, that's not going to be a good bud because I look up the stem and I see this."
Does that make sense? I'm still learning, to be perfectly honest. I'm really reducing my popcorn to cola ratios, but I'm still learning.
I do try to leave the leaves that are collecting good amounts of light.