The purpose of school giving homework to children is to relearn what the school taught in classroom. It helps to build the confidence on solving the question that could bring benefit later in examination.
Indeed assigning many homework could be more harmful than useful, as sometime children can be stressed out due to juggling the imbalance of outside school schedules and homework.
I believe that homework do improve some of the subject I learn when I was young.
Although homework is important, assigning reasonable amount of homework also essential.