Login with two steps / two forms (not meant 2-factor-auth!)

Typical Login-Screens have one < form > element with two < input > (Username/Email and Passwort)

Since last year i see more and more "2 Step Logins". You first have type your username/email, submit the form and in next step you have to type your password and submit again.

1) Is there a name for this method?

2) Whats the main advantage of this technique?