If no caller has requested the pooled session for this many seconds, the pool logs out and releases the vCenter session.
This is enforced by a dedicated timer armed for the exact deadline (not a periodic poll), so the logout happens right at the configured number of seconds rather than some time after it.
The next request will transparently re-establish a new session.
This is useful in environments where idle sessions consume a limited licence slot or where a security policy enforces periodic logout of inactive accounts.
Set to 0 to keep the session alive indefinitely regardless of activity.