The downside with using the IIS option today, though, is that some companies don’t allow full web-servers to be installed on developer machines. IIS also requires administrator account access to setup and debug projects. Different versions of Windows also support different versions of IIS. For example, if you are running on Windows XP you have to use the IIS 5.1 web-server that comes with it – which doesn’t support all the new features of IIS 7.x. Configuring a web project within VS to use IIS also requires some extra installation and configuration steps.
Why IIS Express
It’s lightweight and easy to install (less than 10Mb download and a super quick install) It does not require an administrator account to run/debug applications from Visual Studio It enables a full web-server feature set – including SSL, URL Rewrite, Media Support, and all other IIS 7.x modules It supports and enables the same extensibility model and web.config file settings that IIS 7.x support It can be installed side-by-side with the full IIS web server as well as the ASP.NET Development Server (they do not conflict at all) It works on Windows XP and higher operating systems – giving you a full IIS 7.x developer feature-set on all OS platforms IIS Express (like the ASP.NET Development Server) can be quickly launched to run a site from a directory on disk. It does not require any registration/configuration steps. This makes it really easy to launch and run for development scenarios.