What privacy are you losing? Real question. You're probably revealing to FB or Google that you're a user of web app X, but beyond that? Does using FB or Google auth enable any additional tracking of activities within the app or site? I would think only if the site developer was using Facebook or Google ads or tracking anyway.
Asked another way -- if I sign into a website using FB auth, am I also signing into FB itself at that time? And so can be tracked around the web as if I had logged into FB directly?
Asked another way -- if I sign into a website using FB auth, am I also signing into FB itself at that time? And so can be tracked around the web as if I had logged into FB directly?