This works for small services and apps, but I think it'd be quite a maddening exercise to try and keep a large codebase consistent and organized with that method.
In my opinion it also works for a large codebase. You just have to define your (REST) resources carefully, but they scale very well. The smaller details (on class/object level) are in your lib directory and have no direct relation with your Sinatra app. In fact your Sinatra app could also have been a command line app or something else.
