What is "Create new account" good for?

You can create additional accounts using "Create new" at "Community and Members -> Manage". Such an account can be given away to someone else so those users do not have to register themselves.
Alternatively, you can create additional accounts for yourself, without having to go through your standard registration process each time. Such an account does not differ from an otherwise created account.
The requested data corresponds to what you have defined as mandatory for registration.