When a form is submitted in classic ASP, all form values 
are cleared. Suppose you have submitted a form with a lot 
of information and the server comes back with an error. You 
will have to go back to the form and correct the 
information. You click the back button, and what 
happens.......ALL form values are CLEARED, and you will 
have to start all over again! The site did not maintain 
your ViewState.

When a form is submitted in ASP .NET, the form reappears in 
the browser window together with all form values. How come? 
This is because ASP .NET maintains your ViewState. The 
ViewState indicates the status of the page when submitted 
to the server. The status is defined through a hidden field 
placed on each page with a <form runat="server"> control.

Maintaining the ViewState is the default setting for 
ASP.NET Web Forms. If you want to NOT maintain the 
ViewState, include the directive <%@ Page 
EnableViewState="false" %> at the top of an .aspx page or 
add the attribute EnableViewState="false" to any control.