I don't envy parents trying to ensure their young children get the perfect number of hours of sleep every night. If they sleep too little, they will be grouchy and borderline evil the next day. If they get too much sleep, they will bounce off the walls and be unable to sit still during their regularly scheduled naptime. There is no perfect system, and every kid responds to naptime and bedtime differently.
While some kids grow out of the need for naps early, most kids who are of preschool age at least need some rest during the day. One preschool teacher found herself in a difficult situation because many parents asked her to stop their kids from napping. The problem is that her state's state licensing forbids her from waking up a child who has fallen asleep. Still, the parents persist, claiming that mandatory napping has made bedtime a nightmare.