At my school, generally you would enroll in ~3-5 classes per semester. One or two of those classes would be your "main focus" for the semester, and then you might try to fill a breadth or take something that interests you. You would have a week or two at the beginning before your schedule is fixed to move around classes. So you're not dropping out - you're swapping an Intro to Programming class for something you think you'd get more value out of. I've dropped classes ~45 minutes in to the first lecture because I just... didn't need to take it and wasn't enjoying the professor speak.