Often you want to return data with your call to retrieve a web page/control from ASP.NET MVC so that it can be accessed via JavaScript as a ViewModel (using KnockoutJS or equivalent).
Typically, you make a server call to retrieve the web page using the standard ASP.NET controller action and then make a AJAX call to go retrieve the model to populate your JavaScript ViewModel.
Wouldn't it be nice if you could send back the model with the page request and avoid a separate AJAX call?