David Kimura PRO said over 3 years ago on Reusable Ruby on Rails Application Templates :
  Generators would be something that already exists within the project either through a generator in the lib/generators or from a gem added into the application. This is great for gems to provide installation assistance or for repeatable features. However, if you have to add new features/functionality to your application, the generators are not there for you to consume. This is where application templates can come into play where you add new functionality via an external source.