Firstly, the society in this novel is hedonistic by nature - meaning that the intention of society is to provide people with instant and constant pleasure. By doing this, the leaders have content individuals who will not question their situation.
With that in mind, running the teens ragged is a way to prevent questions and independent thought. At a time when the normal human being is starting to analyze the world around him and come to conclusions about it - not to mention to challenge it - the society keeps these teens so busy as to prevent idle thought. It is, like the burning of the books, a method of control.