Decoupled WordPress is a great use of the REST API, particularly when it comes to using a JS framework. The REST APi really does give you the ability to take data from WordPress, put it into a bucket, and then do whatever it is you want with that data (thanks @mor10 for that analogy).

The best part of this, is once people realize that you can decouple your web application (or website) from WordPress almost completely, they will start to think about what else can be decoupled (maybe there is a better template engine, or better route engine, etc. )