We use nicknames

My question is simple:
Do you need nicknames, logins and what should they be?

For example, on Habr, a nickname is used for identification when displaying messages and as a login, one of the parts of authentication.

And, for example, in Microsoft passport login is email.
It is clear why Microsoft is not asking to come up with a unique nickname - because it is big and you can’t get enough unique nicknames. Well, there are a couple of points, it doesn’t matter. On xpoint.ru, for example, the login is also email. And on drive.ru you can enter email and nickname with login.

Here is the same question, a little wider:
Do you really need a dedicated field for a unique nickname for an account, or can you manage email and make the nickname non-unique, with support for Cyrillic and spaces? For services that require creating a directory on a disk or domain, you can create this most unique field with Latin, no spaces, and so on. On Habr I do not see the need for a nickname.

There is only one problem - user identification. This is so that there are no two different Vasya near and so that no one confuses them.
Maybe someone knows other ways to solve it?

I don’t understand where to post the topic - it seems to be not glued to the announcements of PHP, Opera and tag clouds (webdev). If there are suggestions, I will probably transfer it.