Example: Some apps, you sign in using plain email/password combo, next time it prompts you to sign in and you didnt remember and then you use gmail or facebook, it doesnt matter. anyways the app creates an entirely new profile for you and your starting over from step one. But I dont agree with that, i think its a bad user experience. I would like to say that as long as the email is the same I want them to have access to the same data they set up prior.