I think it's important to read this article (http://www.sunsetlakesoftware.com/2012/02/12/introducing-gpu...) before fully diving into this project. GPUImage (the first version) at a high level gave everyone the ability to create the Instagram effect (realtime video capture and image processing) with little to no effort. Now you will not find "Instagram" in that blog post but I've messed around with almost all of the sample projects in the original codebase and it's hard not to try and create some similar effects, plus I think it's an easy use case to explain to others. With that said, this project goes so far and above Instagram (honestly they shouldn't be compared, but again, easy way to explain it quickly), the use cases are really just limited to what you can think of regarding image processing and rendering.

Edit: Forget my Instagram comparison, Brad gives much better examples in the blog post announcing 2.0: http://www.sunsetlakesoftware.com/2016/04/16/introducing-gpu...