[56k]

I've seen it on a lot of websites.

It's better if you don't remember which email you used to signup, as it validates it right away without you having to enter the password, so you can make multiple attempts more quickly.

It somewhat looks better because after you've entered your email they can show your profile picture.

On Chrome at least, autocomplete still works, so you don't have to enter your password manually if you have it saved. I don't know if other browsers (or even Chrome on certain websites) might get confused if username and passwords aren't together.

It makes it seem easier to login. Having to fill 1 field twice feels better than having to fill 2 fields once (in my opinion, at least).