[devit]

Why would you use this instead of login with Facebook/Google/Twitter/etc., which only requires two clicks from most users and actually has better privacy implication since the user knows which data you can access?

Or maybe the goal of the service is for web sites to surreptitiously get more data from users who are otherwise unwilling to provide it, but are somehow willing to provide an e-mail address tied to their real identity?

[tedmiston]

One advantage from the dev side is not having to deal with the OAuth integration, Facebook permissions, tokens expiring, etc.

[bobbygoodlatte]

That assumes the user is logged in to Facebook / Google / Twitter. That's a safe assumption on desktop, but not on mobile.

We saw much higher FB auth rates on desktop web than mobile—bad enough that we may forego Facebook login on mobile web entirely.