It really depends on what kind of homework you get, and how the teachers implement it in class.
Say you're assigned a book to read as homework, and are supposed to analyze it in class.
You don't need your teachers help to read the book, so reading it in class would be a waste if the time the eacher is avalible, and would either result in less time where the etacher actually teaches you something, or a more expensive education, if you just added the homework hours after normal class and had the teacher there.
If used right, homework will increase the ammount of stuff you you learn durring the time spend with the teacher, and reduce the ammount of time the teacher just stands idly by, while you prepare for what you're about to learn.
If you're just assigned stuff you've done a hundred times before, you'll learn nothing new. This'll most often happen, when you're at the top of the class, and while you're just doing what you already know how to do, someone else might need the prectice to learn it proberbly, and then the problem isn't the homework, but the fact that the level of the class is too uneven, so the good students will be slowed down by the bad students, or the bad students will be left behind, cause they couldn't follow at the pace of the good students.