It really decouples the model (the data that's served in the json) from the view (the mustache template). This lets frameworks like ember and backbone do MVC on the client side where the server is really just there to serve up a model (in the same way that a database does for most current apps).

Making an http request is then equivalent to making a sql query.

Yeah, you'll still need to jump through some hoops to get the data ready. Templates are useful when you have a JSON data source and a rather complex HTML UI that is built off the data on the fly after the page loads. You could totally build the HTML manually inside Javascript as well, but it gets time consuming for the developer, especially with Javascript's lack of long-format strings """like these in Python""".

Thanks for the detailed responses all. Im starting to understand this a little better ;-)