and here's the smarter answer from @tolar: Geofencing typically relies on cell tower changes, a coarser measure of location than GPS, but one that saves on battery life.
So the short story is that we're using geofencing to download news content in the background when you leave your preset "Home" location. Super useful for subway commuters. Kudos to @tolar, iOS developer and subway rider extraordinaire for coming up with it and building it in a weekend.