Well, for one thing, I think a subject like math needs a kid to do some extra exercises just to do some repetition and give the rules that they learned in school some practice. There’s no time for that during class. Other things like essays, reports and projects, while time consuming, force a kid to think on his/her own without just hearing the teacher’s voice and to create something novel, combining things learned perhaps in different subjects. Things can get boring day after day listening to the teacher’s talk.
I do agree, though, that too much homework is a problem, but it’s hard for teachers to coordinate with the whole staff who gives homework that day and who doesn’t. A little bit would not be bad, shouldn’t take more than 1/2 hour on any given day with all subjects, unless it’s a special project and then the teacher doesn’t give any other homework while they’re working on it.