Well, in a word, privacy!
It’s very enticing when you get an invite from a Facebook friend to find out which “celebrity” you are, or taunt you to beat their high score. Please think twice before clicking (no truer words were ever spoken). Game makers often ask for your permission to access your friends as well as the ability to post on your behalf. So, when you take one of the quizzes, remember that you are giving away some of your personal information – along with personal information of your Facebook friends – even those that haven’t clicked the quiz. Although Facebook is trying to tighten this up, it has only been lightly controlled. This has also been a way for malware to infiltrate, but Facebook has effectively shut that down.
Data can also be exfiltrated by bad actors when you use “Login with Facebook.” Let’s look at the following example from Groupon.
These are the default settings if you log in to Groupon using Facebook. Leaving the defaults set is what 3rd parties hope for. Obviously, Groupon needs the user’s name, less so the picture (as an aside, please note that any and all photos used as your Facebook profile picture are public, and remain so, even after they’re not your profile pic anymore). One could make an argument for giving your birthday, maybe they’d send you special offers, but they should ask. There are no reasons to ask for friends, your status updates nor your hometown (current city, yes).
Please go to: https://www.facebook.com/settings?tab=applications and make sure you go through and restrict or remove apps and websites. Remember, it’s always good to give as little info as possible. Please ask yourself “Why would they need that?” Well thought-out sites will have some kind of “why do we ask?” button.