We are used to master pages and applying them to ASPX pages. Then we pull small parts of the view into user controls or ASCX. In ASP.NET MVC, we use ASCX files as partial views because the user control model is so baked into our thinking. I propose that ASCX does not provide much benefit in ASP.NET MVC. It’s usefulness may end with using the extension as a naming convention for the easy identification of partial views. Beyond that, it’s pretty thin.