I've always hated to be over-scheduled. It doesn't happen much anymore, but there was a time when that's all I knew. It's not pleasant and it's not healthy.
I think about the kids I taught in high school who were involved in so many activities. They were in sports, band, had jobs, involved in church and community activities, and then were expected to keep their grades up. Some managed, but so many didn't.
Everyone, children and adults, need quiet, unscheduled time during their day. Parents and teachers need to remember that.