AP Scores in College Admissions

I know that each year, you can ask for the AP people to send your scores to one of your colleges, and that you can send more to colleges for $15. However, I am confused on the score importance for college applications and senior year tests.

If I have taken AP tests my sophomore and junior year, is it a good idea to send them while applying to my colleges? If so, do I re-send scores when I have taken my senior year tests? If i re-send them, will I have to pay both times? Or is it OK to just not send my scores to all my colleges until after my senior year tests are done? Will not sending them negatively affect my chances of admission?

It is not important and most people do not submit official AP score for college application but to the school matriculated after senior year. Self reporting is sufficient and optional.