He might want to reuse his email with a different username that is why he wants it to be deleted.
I guess he has chance to change this account email to a new email or a random email with @bitcointalk.org at the end.
I am not sure but after changing the account email to a new one, he possibly will get another chance to use his original email. But I also think it possibly is not allowed by forum too but he can try.
Make sure that your email address is secure. If you don't want to set an email address, use something like yourUserName@invalid.bitcointalk.org; don't use a random nonsense email like y@x.com, since somebody might create that domain/email.