This is a setting that will affect the web client. If this setting is on, then SharePoint will remember who you are when you move from one site to another. If the Session State is disabled, users may have to enter their logon credentials when moving to a new part or feature of MOSS. The default setting is enabled. This page also allows you to set a timeout period for a user session; the default is 60 minutes. If a user is inactive longer than that, he or she may need to log on again, depending on if he or she is working from the inside of your network or from the Internet.
This option will enable or disable the user session state and how long a session should be maintained. The session state is based on when a user logs in and how long their session can remain inactive before requiring the user to log in again. The default setting is enabled with a session length of 60 minutes. In closed and otherwise secured environments, you can disable this option to eliminate users from ever having to log in more than once.