Depends on age, frame, and other factors, for all weight-class sports. As a general rule, I don't like to see guys remain small, and I certainly as hell don't like to see kids abused by their coaches with assignment to lighter weight classes than they should be in. If an adult wants to stay in a lighter class, fine with me, if it's for the right reasons. Staying artificially light so that you don't get beaten in a heavier class is not the right reason, because you don't know until you've been there that you wouldn't do better at a heavier bodyweight.