what's the reason the application notifies on disconnect?

I ask because I can't imagine a use case for that.

Maybe if I'm using the app and it disconnects I would want to know, but if I left it connected in the background, and here I'm guessing, this is how it happens in 99.9% of cases, and the server eventually kicks out the idle connection, what would I do in response to the notification? Connect it and then leave it idle again?