It is an insult to an opponent to pull your punches.
Ridiculous. I've been on both ends on the tennis court, and it's not fun at all to either run someone off the court or to get killed 0-0. Sports are supposed to be fun, particularly at the recreational level and the high school or middle school level. It doesn't do anyone any good to have one player standing around while the other fires aces past him. What does that accomplish?