As somebody who's never (or almost never) done homework, I have to say that I regret not doing it. I've always understood most of the material being taught and I've always seen homework as a waste of time (this is also a good excuse because I simply was lazy), however I have to admit that the very few times I've managed to sit down and do some homework, it really was useful (but I never admitted it).

Just practicing math problems, or typing out notes and essays, or even practicing a new language... That's all stuff that is useful. Sure you can go without, and probably schools assign way more than they should (I know it was the case for me), but homework itself at least is not a negative thing.