If you do not add "System.RunWhenNotFocused = true" to your psclient.cfg file, whenever you click on another application PS will show as [Pause]. Note that the world is not put on hold, but only your character. So any loading you might be doing will freeze and any other activity you might be engaged in, as well. It should not make you crash but it's kind of a pain if you like to run several programs at the same time.