One of the use cases for ST.js in Jasonette is dynamic client-side rendering, where it takes dynamic data and renders it against the template, after which it becomes native components.
Another use case is implementing actual functional programming. This one is not as straight-forward since it involves maintaining another separate state machine for function call stack. But this is also achieved using ST templates. Here's a blog post that talks about it in detail http://blog.jasonette.com/2017/02/15/functional-programming-... but it's a bit involved.
Also Jasonette has something called mixins, which you probably can guess based on its name. It lets you mix in JSON objects into another, so that you can make the app modular. That's also achieved internally using ST.
Overall, I believe even I'm just scratching the surface of what this can do, which is why I decided to take some time to clean things up and prepare and open it up as its own repo, because I think there's tons of other things that can be done by taking advantage of the fact that all that's happening is:
JSON A + JSON B = JSON C
Hope this makes sense!