I think that what happens is that when people cut for pics, competition, personal reasons, ect...they have one goal in mind...getting cut. Either way, when you cut, you loose volume. Nothing you can do about that. The volume and little bit of fat around your chest, arms, and lats, gives you a nice little volume...you just look huge. It would be nice to look like that, but emit the fat around the belly. Unfortunalty, that is impossible. So when you finally achieve that physique, wether you were lifitng heavy or not, you got shredded, and are happy. But bodybuilders after years of expereince, they know that they want to have as much muscle fullness as possible. It's tough to maintain that muscle 'MASS' by lifting light. Some feel that there are so many drugs in your system, that no matter what you do, you know you got back up and won't loose that much muscle. As for me personally, I have never gone light even when cutting. I do kill at the end with more reps sometimes to burn the shit out of my muscles on some days and make me feel like crying, but thats after my heavy lifting. But as I said, many get the look they want with light reps, and hey, if it aint broke, then don't fix it. But I do understand the "bodybuilding" aspect of preserving the size of the muscle. I guess to each his/her own.