As a user, there's absolutely no way I'm going to give you a real name and email address if you roll your own authentication. I probably won't use your service at all.

Why not? Saves you the trouble of building and maintaining a secure access system. You likely gain more users because of network effects, which doesn’t cut your advertising budget so much as supplements it. If your trying to preserve user privacy, there’s a good chance you’re too late there - they most likely already gave that up a long time ago.

When you use a federated login, you still can assign an email address to the federated user. Most of them will even pass one to you.

But, do you really want your users to have the added friction and probably just move on to another site, and do you really want the responsibility of providing your own authorization? I work for a B2B SASS company and we highly encourage users to use their company’s AD account that we federate with.

What are you using for analytics or ads placement?