I almost threw myself out the window after seeing that hard-coded HTML in a JavaScript string. How is that maintainable or even nice to look at? It's not.
Am I crazy? What is the benefit of this? With a bit of customization rails could do this out of the box without a duplicate MVC arch.
Before long you're going to have a real mess of Javascript variables, DOM elements and arrays of stuff, which is why it's useful to have MVC structure on the client as well as the server.
Your server models sync automatically to your client models, you can hit model.save() to persist your client models, and your client views represent the data in a way which can be quickly adapted if requirements change.
For a less dynamic app you don't need it.
You actually don't need to hardcode the html in the javascript. You can use a template system that is already included in backbone, or you can preform a request to the server,
I prefer the first approach.
I can tell you know that after using Backbone for a largish javascript project, it really eases the pain that comes with syncing data to and from the server, and handling all the random bits of javascript that usually pile up in a Rails application.
Basically, it gives you a logical place for everything.
Of course, if you're app isn't javascript intensive, there's no reason to use it.