In reply to Dudeski.

To expand on what John Teague says:
You could use WP as the data storage for native apps. Since the data will be more easily retrievable you can then fetch it for anything. You could probably use it to store data in games even (granted, there are probably much better solutions for that use case).

A more WP applicable use case is the infinite scrolling wall. yes, you can already do that, but with a RESTfull approach you can load your page and then only load new posts when you need to. Or you can load pages without a full page reload, letting you animate the page load inside your site. Essentially everything you want to load, but isn't shown directly without the user's interaction can more easily be defered to the point where the user actually wants to see the content.

The reason the WP REST API is such a big deal is that it marks a change from full page reloads being the standard, to a much more flexible data driven design.