Social Login and Social Plugins Increase Page Views, Time Spent On Site
blog.gigya.com
blog.gigya.com
Additionally we found on our site that social login increased conversions for signups but those people are generally of lower value to our freemium product in the long run because they're less likely to want to pay.
In fact I "deleted" my Facebook existence and if you want to force me into a social login, any social login, you just lost me.
Your mileage may vary, of course.
b. post hoc ergo propter hoc fallacy committed
c. I trust Mozilla more https://news.ycombinator.com/item?id=5408735
And users who use social login will perhaps spend more time if it's not provided.
Any "friction", like having to enter a username, email and password is three more steps than a social login requires, costing these casual users.
So, I can believe it is highly effective for specific applications.