Gotta love the innocent data mining in various online services.
You don't need to give us anything but...
... if you give us all your contacts, we can tell you which of your friends are here!
... if you tell us your birthday, we can congratulate you on your birthday!
... if you agree to receive our newsletter, you won't miss the best deals!
... if you add your friends to this service that is not social in any meaningful way, you'll know what your friends are up to here!