I took 3 AP classes my senior year. My thought behind them was if I do well, I'll send them, and if not, I won't. I got two 5's and one 4 so I sent them. While I don't think they can hurt you, good AP exam scores show that you are capable of excelling in a college level course and therefore can excel at the Academy. During my nominations process I found that having these scores on my application was also a big help. Having the courses on your schedule is important, but at least a 3 on the exam is beneficial. As far as I know, you can't use those scores to exempt out of certain Plebe courses, you can only do that if you do well on the entrance exams over Plebe summer.