We’ve touched on the differences between OpenID and a traditional login flow. In short, OpenID provides a number of advantages over a home-grown solution.
One of OpenID’s greatest benefits over the traditional login flow is how accounts are created. With OpenID, since you are leveraging the user’s existing account on a different site, you don’t need to require her to create a new account when she first visits your site or service.
Using the login of another site as your base, you can create a default profile for the user with her linked account information and email address. With that, you can allow her to use your service and prompt her to flesh out the base profile with the rest of her details.
The topic of filling out the user profile brings us to our next point: using OpenID to build a rich social graph.