In ASP.NET Web Forms if you want to use jQuery and call a method directly, you should either implement a web service, or use Page Methods. Also you can use Generic Handlers (.ashx files).
However, in ASP.NET MVC, a controller action (a method in nature) can be called directly from jQuery.
What web services has to offer in ASP.NET MVC world? In other words, seems that I can fulfill of my requirements via MVC's clean URLs, controllers and actions. Should I bother using Web Services?