Homework is like any assignment or task at work, only that if it is too much, it could cause fatigue. Homework could include blogging, wiki authoring & collaborative writing, apart from the traditional assignment of book reports, completion of worksheets or projects.
There might be correlation between the amount of homework with the assessment score, but I reckon it’s the quality of homework, feedback and reflection that matter most, in improving the performance and learning. Practice makes perfect is only “true” if practice (like blogging, cycling) is followed through a learning cycle of plan-do-check-act or “trial and error” with feedback.
For me, I think an adequate amount of homework for the young kids is necessary, to reinforce their learning. Too much homework at a young age may demotivate kids from learning, especially if such homework is based on routine rote learning. Stimulating, interesting homework (such as blogging, wikis, forum postings and discussion) for teenager and adult students might be better alternatives, though this again depends on individual needs.