The precise location aspect is what I like, I know where I am on the aerial photograph, but no one else does (except in a general sense-OB's out on the XYZ alignment). I carry the cell phone when I'm in the field, otherwise it's in the vehicle. Though it isn't on unless I'm calling someone. :-)
Plus, without the precise coordinates, how is Chloe going to find you and download the locations of the bad guys to your PDA?