Ah, Kindle Scout
Amazon built this program to replace their old competition where they selected certain books to publish, and it was designed as a rolling enrollment system where people can load books at any time and have a chance at getting a publishing contract.
A lot of authors have broken down the system, and there are even a few guide books about the system that can be hugely beneficial.
Basically, you get an advance, great access to rights, and targeted promotions as part of the campaign. Most authors have come to the conclusion that the system is worth it and that they could benefit greatly from winning a contract.