This is about learning how to learn, so this is mandatory reading.
I believe one of the leading predictors of success in life is being able to assess your weaknesses and be able to remedy them. MAST is supposed to provide a new perspective on how to learn math on your own.
It's not the only way to learn math on your own, and I weakly recommend against only doing MAST for math. (In particular, only doing my material is substantially better than doing no material.) But I do recommend doing stuff other than MAST to study as well, if possible. Learning how to learn is about synthesizing some amount of crude information in your head - this is easier if you synthesize the techniques for synthesizing information.
I'm not specifically teaching you what you need to succeed in the AIME - I'm teaching you how to teach yourself what you need to succeed in the AIME. I'm here to help, but in the case of math competitions, the only way to get better is to do most of the heavy lifting by yourself.
This is not mandatory reading, but is hopefully interesting enough to read anyway.
I think math competitions emulate the "real world" much better than school. In school, there are always enough resources for you to succeed. And there is a real attempt in school to make it so effort always leads to success. This is not the case in the real world, and is not the case in math competitions.
Math teaches you a skill more important than putting in effort to succeed. It teaches you how to put in the effort to succeed in spite of the fact that you may fail. It teaches you to be resourceful, because there are no other choices. It forces you to consider things from other peoples' perspectives - you solve a problem when you figure out how to think about it. Math competitions teach people to sort out stuff that works from stuff that doesn't, which really helps with communication - it helps you sort out which of their ideas are good, and it makes you valuable because you can sort out how good other people's ideas are.