Does 'quit' have a place in iOS apps?

[Graham Samuel]

AFAICS, iOS apps don't have an overt 'quit' button, since simply pressing the physical button on the device (I forgot its name) quits whatever is running. However this isn't quite right is it, since apps can go on being present and maybe actually running in the background. And then there is the question of what happens when your app gets itself into an unexpected state and has no alternative but to exit, which presumably would mean using a 'quit' command. Again, from the slender evidence I have, an explicit 'quit' may cause iOS to restart your app, tho not apparently in all circumstances. I have not yet found out the difference between stopping and leaving the app running in the background and really killing the app.

Has anyone a clearer picture of how and why one would use 'quit' in the script of an iOS app?

TIA

Graham