Depends what kind of homework. A huge portion of school is just there to learn how to learn. Learn how to teach yourself something. Getting the fundamental basics of knowledge and how to tackle subjects that are strange, foreign, boring.

Some things you'll have to learn by yourself. Students between 5 - 14 are just not there to learn vocabulary, basic maths, etc. on their own. It gives every student the chance to do it at their own pace, find their own way how to learn and understand it best, using the tools they learned during class.

That the execution of this theory is not the best (especially in certain countries) is obvious, however, I think without homework I would have no tools nowadays to get into a new, complicated topic without being tutored/ guided all the way through.