Comment by hallway_monitor

Yes this is a use case but I would hardly call it the common one. I agree with GP, it really makes things harder to read not knowing if it's an actual method on a class or just a static helper function with syntactic sugar on top.

I have begun writing all static method calls as static method calls even when they are defined as extension methods. It's a little less terse but that's worth the decreased surprise. You can do this with the ASP.net configuration calls as well.