Contacts on what? Your comments makes it sound like it will use its authorization with a Google Account to send spam. And I just clicked the permission button 30 seconds before reading it.
More specifically: I connected to Quora using my Facebook account. When I connected, within the Quora system the message "Viliam is following your questions and answers" was sent to all Quora users who are also my Facebook contacts.
As far as I know, it didn't do anything outside of Quora. But even this is kinda creepy. I discovered it when one of those users asked me in a FB message why exactly am I following his questions (in given context, it seemed like a rather creepy action by me). I didn't even know what he was speaking about.
So the lesson ...
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.