For small web pages (not web apps), as well as web apps that don't involve much JavaScript -- you're absolutely right, there's no benefit in using Backbone.js.
The idea with Backbone is to provide structure for large JS applications that involve manipulating state in the client. Too often, they can devolve into jQuery spaghetti, all updating a nested global JSON object. Backbone models provide a large number of data manipulation functions (map, reduce, filter, reject, any, etc...), RESTful persistence for your data, as well as events you can hook into, so that your models and views are notified whenever the state changes.
In the end, instead of peeking into a blob of JSON, tweaking the DOM manually, and making a $.ajax call, the hope is that you'll be able to write:
note.save({title: "Lorem Ipsum"});
... and all of the UI currently referencing the note automatically updates, and the changes are saved to the server.
I'm afraid I can't give you anything informed ... as I haven't used either of them in anger.
That said, they take a very different approach: less about data modeling and events, and more about binding JSON structures tightly to specific DOM elements. I have my own concerns about if it's possible to build truly high-performance web applications with such a granular scheme -- for example, Knockout.js calls JavaScript's "eval()" on every "data-bind" attribute in your HTML. But without someone taking the time to port the same app to all three libraries, and then evaluating it with benchmarks, it's all just speculation.
The idea with Backbone is to provide structure for large JS applications that involve manipulating state in the client. Too often, they can devolve into jQuery spaghetti, all updating a nested global JSON object. Backbone models provide a large number of data manipulation functions (map, reduce, filter, reject, any, etc...), RESTful persistence for your data, as well as events you can hook into, so that your models and views are notified whenever the state changes.
In the end, instead of peeking into a blob of JSON, tweaking the DOM manually, and making a $.ajax call, the hope is that you'll be able to write:
... and all of the UI currently referencing the note automatically updates, and the changes are saved to the server.Also, note that Backbone has quite a different philosophy than Sammy. For more on that, see: https://hackernews.hn/item?id=1887563