ScrOG - The whys?

I understand the idea I believe, which is to level the playing feild to even out the light distribution and to spread the plant out to keep each branch top in good light. About trimming everything below the screen, I don't quite understand this. Why not trim some fan leaves to allow the light to penetrate down to lower bud sites? Or does trimming the lower stuff create THAT much of a gain in the tops?

you remove the foilage under the screen, including the buds to make the plant focus its energy on the top colas.

Bythe time the screen is full you would have to remove an excessive amount of fan leaves for your light to get through to the growth under the screen. Your plants create energy with those leaves so the more you remove in the light the less the plant has to work with. If your plant is trying to put on growth under the canopy in the shade it is wasting energy it could be using to create fat, juicy buds