Originally Posted by Jbrandes
And that's the same whenever you leave your computer on a certain amount of time it automatically logs off
Is that a question? If so it depends on your system configuration; most systems go to 'sleep' after a certain amount of time and locks your account once it wakes.
While it's not impossible to configure a system to log off at a set given time of inactivity, it's not something I've really seen anyway.