When I turn my GPS feature on in my 6D, the battery drains very quickly.Smartphones are bound to be more optimized than this, but for a dumb device you'd better turn gps off in difficult situations.
It's been my experience that any GPS application is a rapid battery drain. Even an hour car trip on a top line Android with GPS enabled the entire time can drop you down to 50%.
The GPS feature on the 6D is kind of a bonus but I don't think I will use it. Maybe it would be useful to tag the first photo of a set to mark them, but in all honesty, it's just as easy to tag your own images and excepting industrial applications for Long/Lat in a consumer level camera, I don't see the point.
However I'm glad someone brought up the grip - It's my opinion that two batteries (one acting as a critical spare) is a bare minimum. Why not add the joystick plus the extra grip and add the option to use AA's?