6th
The REST support in Rails emphasizes the convention of CRUD operations. map.resources gives you a fistful of named routes that have built-in knowledge of CRUD action names. The emphasis on CRUD at this level encourages you to think of modeling for CRUD. Instead of having, say, a users controller with a borrow_book action, you can have a loans controller with a create action. In many cases, this way of thinking might also wag the dog of your domain modeling. Thinking about CRUD in the controller might, for example, lead you to conclude that you should have a Loan model.
It’s perfectly fine—indeed, in my view, it’s very productive—to think along these lines, to bring your modeling and your REST-friendly CRUD operations into harmony, as long as you understand that none of this is actually about resources as such. Rather, it’s about the Rails flavor of implementing the handlers that underpin the creation of resource representations.
Does that sound like just a lot of extra words? It isn’t. It’s a lot of words, but they’re not extra.