From what I can see, it triggers at odd times, which makes addons utilize extra cpu time for no reason.
A good example I have been made aware off, is if you run between the wayshrine and the guild traders in Belkarth.
It triggers around the bridge every time, but there is NO changes in the values it returns, and I already know all POI's in that zone. It doesn't even change between zone/submap.
Does it have to do with distance to POI's?
Whenever that event is fired, the worldmap removes and re adds all the poi pins. As undisovered POI are only visible when being nearby, I guess it's really just a distance indicator. It probably fires every time the player crosses the visiblity radius for a POI.
Earlier when I read the post I thought to myself "how cool would be if Chip himself commented here" and now my dream has come true. Thank you Chip, you're the best.