I'm not sure what is "useless knowledge?" If you mean knowledge that you do not put to use, as I suspect, then I couldn't disagree more. The process of acquiring knowledge is itself useful. When you put your mind to work, even if it is the act of memorizing or remembering, you are, in effect, using your brain. As with almost any other part of your body, disuse is unhealthy. Now, having said that, too many teachers concentrate on the "what" rather than the "why." One should use the "what" in order to explain the "why." That is where intellectual discipline enters.
Personally, I think that college students who have not taken math (calculus or higher) or studied grammatical syntax have missed out on magnificent tools which provide mental discipline. There was a good reason for requiring Latin and calculus in high school, and it is painfully obvious that the end of such requirements has done our country a disservice.
No one has the right to demand aid, but everyone has a moral obligation to provide it-William Godwin