Can anyone get me a detailed answer on this?
What's the advantage of using Session-less Controllers in ASP.NET MVC?
If you have a Session-less Controller then you will be able service simultaneous requests from the same browser instance. Otherwise, ASP.NET will queue up the requests as they are received in order to give them sequential access to the ASP.NET Session object, to avoid deadlock issues or other race conditions.
You can actually have 1 request to a 'Session-ful' Controller and multiple requests to 'Session-less' Controllers simultaneously. This pattern has been useful to me in implementing a long-running process (implemented through a 'Session-ful' AsyncController) with AJAX calls from the client to a 'Session-less' Controller which provides the user with updates as to how far through the long-running process the server is.