Beta testing is a pretty big part of developing iOS apps these days. Once upon a time, a developer could throw an app out there and fix bugs as they went along, but with competition at its fiercest these days, that would be suicide for most. Most apps have so much competition, users will just move onto the next big thing, or find a replacement that works better. Bugs kill apps, and dead apps kill developers.
Beta testing is vital, and Testflight makes it super easy for both the tester and the developer alike...