The reason to provide Application object in ASP.NET was primarily backward compatibility with the Classic ASP so that it is easier to migrate Classic ASP application to ASP.NET.
It is recommended to keep the application wide information in static variables instead of Application Object, because static variables are faster than you can access an item in the Application dictionary.
More Information : http://support.microsoft.com/default.aspx?scid=kb;en-us;Q312607
