While it would be good, kind of almost seems like unecessary posts sometimes, there are a few flaws in it. Firstly, the obvious one, it could get kind of confusing if people were to just pop in and out of places at will. If, say, you were following someone, you'd have to check each location until you finally found them. Secondly, if, say, someone wanted to talk to you in a certain post, they wouldn't even really know you'd left unless they tracked individual players' activity in other locations.
There are probably a bunch of other things but... Well, yeah. Still, a good idea Dragster

Just, don't get your hopes
too high on it being implemented.