Research does NOT clearly show homework has no positive effect. The studies are many with contradictory results.
http://www.districtadministration.com/article/homework-or-not-research-question
https://www.washingtonpost.com/news/answer-sheet/wp/2012/11/19/study-homework-linked-to-better-standardized-test-scores/
http://www.centerforpubliceducation.org/Main-Menu/Instruction/What-research-says-about-the-value-of-homework-At-a-glance/What-research-says-about-the-value-of-homework-Research-review.html
IMO homework is useful for the most part. It should strengthen things learned during school. What some consider busy work (do they really need to color things on their paper?) other students gleefully do because that’s what tickles their personality. I also think some of it is giving chances to the not so smart kid who needs some points to pass. There is something to be said about a persistent student. They may do better in their career than the quicker student because they carry things through.