We use nicknames

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

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

And, for example, in Microsoft passport login is email.
It is clear why Microsoft does not ask you to come up with a unique nickname - because it is big and unique nicknames you will not save enough on it. Well, there are still a couple of moments, it does not matter. On xpoint.ru, for example, the login is also email. And on drive.ru, you can email and nickname enter login.
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Here is the same question, a little wider:
Is a dedicated unique username login field really required for an account, or can emails be avoided and can you make a non-unique username, with Cyrillic support and spaces? For services that require the creation of a directory on a disk or domain, you can create this most unique field with a Latin, no spaces and so on. On Habré, I see no need for a nickname login.

Only one problem - user identification. This is so that there are not two different Vasya around and that no one confuses them.
Maybe someone knows other ways to solve it?

Where to post a topic, I do not understand - it seems that PHP, Opera and tag clouds (webdev) are not glued to the announcements. If there are offers, I will probably transfer it.