My elementary school best practice: Homework that exists because it adds demonstrable value and could only be done at home, primarily due to needing parental involvement (i.e. one-on-one mentoring). In younger grades that would mostly be reading out loud. As they get older, it could encompass more research time for projects, and parental engagement that allows for more discussion of ideas/ depth/ complexity to projects (but not the complicated construction/ crafting busy work often mentioned on this forum).
Otherwise, if there's no reason the work couldn't be done at school, then there's no reason the work couldn't be done at school.
I do know some parents who value homework because it allows them to quickly identify if a child is struggling with a new concept. Optional homework could address this need. But even better is just good communications from the teachers. One of my favourite examples was "Ask about". Every week, the teacher would send home an e-mail, saying "ask your child about.... the following things we did/ discussed this week." If you added on a sample sheet of new concepts, bingo: parents know what's happening in the classroom, have great conversation starter with their kids, plus the ability to double check comprehension should they feel the need ("oh cool - you learned two digit multiplication this week? Show me how that works!".
