Not every web application needs to use Session state. Disable Session state for sites that do not make use of it. The performance improvement may be very minimum, but cutting down extra processing for every request is always good.

Session state can be disabled in the web.config file:
<configuration>
   <system.web>
     <sessionState mode="Off" />
   </system.web>
</configuration>

Session state can also be disabled on individual pages by modifying the "EnableSessionState" page directive on each page.