It's probably just for their Location History thing. Which I actually really enjoy using, since I can see all of my past days and where I went. It's pretty neat.
I've been using this feature for so long I assume it's opt-in (I don't remember), but I fully recommend it to anyone that has an inkling of a thought that they _might_ want it later, since you can always delete[4] your location history if you decide you don't.
It's also really cool if you go on a lot of trips or take a lot of photos, because it'll map them out in a timeline view of where/when you took them throughout the day[5].
[1] http://i.imgur.com/gWzMgUp.png [2] http://i.imgur.com/Eq7IGnK.png [3] http://i.imgur.com/HEeZupJ.png [4] https://support.google.com/accounts/answer/3118687?hl=en [5] http://i.imgur.com/dF5TI3q.png
Get rid of your toys before your toys get rid of you.