According to msdn ASP.NET Web API is a framework that makes it easy to build HTTP services that reach a broad range of clients, including browsers and mobile devices. ASP.NET Web API is an ideal platform for building RESTful applications on the .NET Framework.
Fig: Asp.Net Web Api Processing Architecture
Today, a Web- based Application is not enough for real world Because People are so much smart they using different kind of device and mobile in daily life like iPhone, tablets and embedded system. These device have lot of apps for making the easy life. Actually we are moving from the web toward Apps World.
Suppose Client Need to develop Sales Application. But this application will support Mobile version (Mobile Application) and web application. In this scenario if we use Asp.net Web API then Client Requirement will be fill up.
We can see that above Picture different type devices and browser are doing http request to Web API. It’s fully platform independent. We can use API different Platform