I am not clear that what is the purpose of running asp.net application in IIS. Why we go for IIS. Any difference amoung running in VS and IIS?
Please suggest me.
Simply because you won't run asp.net in VS on production !
IIS Express and the VS Development Server are designed to emulate IIS, but they are configured differently and may fail to reveal errors that can occur when you deploy to a production version of IIS.
Visual Studio Development Server, also known as Cassini, is very limited. It does not have all IIS features and we will have a few problems when resolving References to Root-Level Resources or on security.
For example, when you run a page using IIS Express/VS Development Server, the page runs in the context of your current user account (often Admin). In IIS 7, by default ASP.NET runs in an account that has limited privileges (know as AppPool Identity, see here). This difference can be a source of problems when you deploy on production a web application.
A complete list of Hosting options is available here.