Today I discovered by pure chance an useful feature in Git.
If you ever changed either your name or your e-mail address (or both), you noticed a problem in Git: While you can change your config file to change your current name and e-mail, your old name/e-mail is still present in old commits. This can be really annoying for many reasons.
But Git has a feature called "mailmap" which basically is just a special file in which you can specify the canonical name/e-mail to be used in place of the old undesired name/e-mail. This technically is like an alias. This affects things like e.g. "git log".
While this does not completely erase your old identity from the system, it's still better than nothing.
I am starting to add a mailmap in my git repos because I changed my e-mail.