Areas have been a part of ASP.NET MVC since ASP.NET MVC 2 shipped in 2010. This walkthrough article from MSDN sums up why areas are useful in MVC web applications. A brief extract follows:
To accommodate large projects, ASP.NET MVC lets you partition Web applications into smaller units that are referred to as areas. Areas provide a way to separate a large MVC Web application into smaller functional groupings. An area is effectively an MVC structure inside an application. An application could contain several MVC structures (areas).
For example, a single large e-commerce application might be divided into areas that represent the storefront, product reviews, user account administration, and the purchasing system. Each area represents a separate function of the overall application.
The release of Sitecore 6.6 saw the introduction of support for MVC and the Razor view engine within the Sitecore CMS. It wasn’t long before a question popped up on stackoverflow asking how to wire up a Sitecore Controller Rendering to a controller located within a MVC Area.
Hopefully this article will provide some answers for those wanting to use MVC Areas with Sitecore and highlight a few of the subtleties that currently may not be so well documented.
Stone Soup Developer 