Earlier quoted context omitted.
So after 20 minutes instead of logging you out the away status is set. Not sure I understand your special case here.
I don't see what's not to understand or what logging out has to do with it. I have a browser tab for an IM application, that's also available as a native app on my phone. That tab is always open on my desktop. If I have other tabs open and am doing stuff, I still want my IM status to be 'available', and I want all notifications about new chats to go to that tab and to no other devices, while I am on my computer doing…
That's a setting within the chat app/website. Always remain online vs make inactive after 20 minutes or 4 hours.