android phones automatically sync with your google account. this ties the phone with maps, nav, gmail, appstore, etcetera. having to sign in & out would be really irritating.
if you're worried about other people accessing the information then you have a few choices:
-set up a password on the lockscreen so that only you can access the screen.
-set up a gesture lock password to unlock the phone
-get an app that locks down the screen
-manually set your phone into "locked mode" whenever it will not be on your person. this way is probably most convenient.