It's a bit like saying: "Oh, by the way. I might be hanging out down at the bar tonight. Swing by if you feel like it". Without actually having to say it out loud.
edit: The more I think about this, the more angry I get. It feels like the Google+ nerd mafia is slowly destroying Facebook through bad influence. They simply don't understand how and why Facebook works and is popular. The whole privacy and circles stuff for example, which is just stupid. No normal person cares about that. Facebook is a tool for sharing and connecting and to limit that in the name of privacy is insanely counterproductive. It only adds a wet blanket of politics on something that is better understood through social psychology and sociology. Facebook used to understand that, but now it seems they've started to become distracted. Sad really.