I thought I was already one thread said Yes, but the answer was not among the above(although I read it diagonally).
The problem is that people make mistakes, sometimes inserting your address is incorrect. Yes, auto-completion is not everywhere and not always works(corny due to the fact that the name of the input, otherwise), do not have your computer, the person chooses not to remember such data etc.
Higher people say that it does not matter if the user makes a mistake. However, these people, apparently, not so often recorded or simply not been in a problem situation.
And the problem can be as simple as two fingers and called: "sorry, this username is already taken".
Yes! Most services offer at registration to enter a username, nickname or other unique information. If you enter the wrong email address and correct unique information that is no longer required to register under your username, putting your wallet, using your account address on lastfm or Habra etc.
The biggest problem when working with a minimalist services, where there is no need to register, but where you must specify the mail after all the action, so they are not misplaced or to alert. Enter the wrong soap down the drain.