basically if you have it set to off, it'll never shutdown unless you do it manually. It won't shut down normally if you're recording with it, but if its just sitting there doing nothing and you have idle shutdown active at like 5 mins for example, it'll shut down after 5 mins. This can be handy if you're forgetful and don't want to waste batteries.
i usually have mine set for 5 minutes, cuz at the end of the show when i stop recording i just start throwing stuff in the bag so i can get the hell out of there, or i'm a bit too drunk to pay attention to some of the details. i get forgetful at times, so its handy to have it on so if i forget to turn the nomad off, it'll go off automatically.