Every chat user can invite another chat user to a newly created room using the "start a new room with this user" button on the chat user profile. This will ping or notify the user in the global inbox (as far as I know) and invite them to a new chat room.
I don't think this feature serves any useful purpose, inviting a random chat user into a new room is something one should almost never do. And for users you know, pinging them in a room you know they are usually present works very well.
The only time I was the target of this feature was from a user abusing it and randomly contacting multiple people. Everyone who has a reason to contact me either knows which chat rooms I can be found, or will check the regular room of the sites I'm a mod on.
Now, a user can of course abuse the regular ping in an existing chat room to achieve nearly the same effect. But I think this feature still sends the wrong message, that inviting someone into a new room is something that is somehow encouraged.