Lots of apps use the GPS. Even the browser. If you're indoors, don't care about GPS and want to browse, turning GPS off will save your battery some life. Otherwise, the browser will try its damnedest to get a fix.
It's good to have choices.
Websites have to request access, they cannot just start using your location randomly. Google.com might be enabled by default, but you can also edit the sites that are allowed to request in your settings menu for the browser. You can also check the box that allows NO sites to request your location. GPS uses 0% battery when not in use, so turning GPS off when it was not in use will not save you any battery.