Back in the day when Soffee shorts were the thing to wear, we always had 4 screen printed shirts and then a designated matching Soffee shorts color(which were common colors such as black, grey, navy, or school colors so that everyone had at least 1 pair, if not more). Since we had practice during school Monday through Friday, then M,T,W,Th all had a shirt and shorts color that we wore every week. Friday was a free day so we could wear whatever in practice. Any additional practices fell on that rule, so if the practice was added on Monday after school, you'd wear the "monday outfit". If the practice was added on a weekend for competition or something, then it would also be a free outfit day.
I will say that while you don't need matching outfits to make a good routine, it is certainly easier to see visually what's going on and also to clean in my opinion. Additionally, the sooner that girls learn responsibility (wearing the right clothing, showing up on time, etc.), the better prepared they will be for life past high school I believe, so I am all for having the girls required to wear certain outfits!:)