Hello! (Truth in advertising, I'm an ALO.) Your ALO can help you to get an appointment by answering questions on the Academy, life as an Air Force officer, and the admissions process, as well as mentoring you on the best ways for you to prepare and become more competitive. If you have a lot of questions, he/she can help a lot. If you already know a lot about the Academy and are already on a serious college-prep track, then there may be less of an impact for you. Of course, the earlier in the process you contact one, the more help you can get. It's up to you how much interaction you have.
He/she will also do an interview you at least once (more is better) and write a report. This interview provides you the opportunity to communicate directly with the admissions panel and add subjective or intangible items to your application. Here's the USAFA page for more info: http://academyadmissions.com/admissions/preparation/alo.php.
Hope this helps.