Enforcing payment comes to mind without resorting to in-app purchase or any account creation. A lot of desktop software is a good example of those. Sure, you can still have cracks and whatnot, but then again, that’s not the point. Might as well ask what is the point of Denuvo. That is a whole other discussion.
Nothing comes to mind. DRM literally means digital rights management and unless you wanted to be petty, like blocking a certain person from using your app, then DRM for something free is not something that I can think of a use case for.