Excellent description. LOA are basically just the academy's version of "Early Admissions" that ALL COLLEGES DO. There's a few additional rules and such, but the concept is basically the same. Colleges take early applications and run them through an early acceptance process. They've been offering acceptances for many years now. Same with the academy. They know what the average in EVERY category is going to be for those who get accepted each year. I.e. The incoming class of 2013 is going to have very similar gpa, ACT/SAT, EC, etc... as the class of 2012, 2011, 2010, etc... But they can tell those that are considerably above those averages.
Just like any college, the academies want you to commit early. The sooner they can get a person to commit, the more excited that person will be and more of a chance they will accept the school. That's exactly what the other colleges did/do when putting out early acceptance letters. They are trying to get you really excited in the fall of your senior year in the hopes that you will sign and register with their school.
Realize however that the ONLY thing you as a candidate can do towards an LOA, is to have your application 100% as soon as possible. And I'm NOT TALKING about by November. I'm talking about having it 100% complete by the first part of September. If you think back hard enough, you might remember an email/form/letter/etc... when you were first being notified about your online application. It mentioned being considered early if the APPLICATION WAS COMPLETED WITHIN 45 DAYS!!!! Yes, that is very difficult. Not impossible. Complete doesn't include the Nomination and DODMRB waivers. But those are the applications that get looked at first. If they are high above the averages based on years of data, and the academy wants you, they will offer an LOA. Unless of course you already have a presidential or other nomination. Then an LOA isn't required. They will offer you the appointment directly.
LOA's are for many reasons. But mainly those that are very early in the application process; has a total score that based on history will put them in the top percentage whether they look now, 2 months from now, or wait until March. There are a few LOA that will be given out throughout until March, but those are very specialized.. The majority are given out in the fall and only include a couple hundred. There's a lot of different people applying to the academy. Not just the typical high school student in their senior year. There's college students; Prior enlisted military; ROTC students; students living overseas; students from U.S. Territories (puerto rico, virgin islands, guam, etc...); medical turnbacks from last year; etc.... Then, take the auto-principle nominees that each rep has (When applicable and eligible); and the process gets very interesting. I.e. 2 candidates from the same district. Both walk on water. Only one can get a principle nom. But the academy REALLY wants both. Give them an LOA to give the MOC the ability to get both in. LOA are small in number but is a powerful tool for the academy to get the best of the best and used as an early admissions tool.
Remember; there are few things you as an applicant can do to increase your chances of an LOA. Get your application finished before September. The next thing you can do is to be the top percentage academically and in all other areas. I.e. the top 1% in your class; not the top 10%. Varsity letter 2-3 sports, not city league sports. All AP/IB classes, not just a couple classes a year. I'm not say that these are the only people who get LOA. They aren't. I'm talking about what YOU THE APPLICANT can do to increase your odds of being offered an LOA. Best of luck. Mike....