User names are useful in a team context: when you see who created a file or who is currently modifying the file with you. Also when receiving the email invite t

User names are useful in a team context: when you see who created a file or who is currently modifying the file with you. Also when receiving the email invite to a team / project. Otherwise, you'd have to display the full email, which isn't as readable. Using social logins would definitely help in making the sign-up simpler (but I guess you still need it in the form if using email login option though).