You can use it to inhibit overactive myofacial tissues. It's also used to help alleviate trigger points, which are like knots, and are very sensitive to pain and pressure. Scar tissue and other adhesions can also be worked out. In the end, the length-tension relationship of the muscle in question is improved. The end results is an improved length-tension relationship in the tissue and hopefully corrected muscular imbalances and motor patterns.
I use it on myself and virtually all of my clients. I warn you that it hurts like Hell. The first time you do it you are going to fucking flip when you roll your IT band/TFL. I have a couple of clients that I cannot convince to use it because they are whiney bitches, but most of them concede and start to like it/accept it. Once you do it consistently for a bit the pain won't be as bad.