The Gnu Emacs for Windows distribution appears to be pretty good at inferring where a reasonable place for $HOME is, straight out of the box. In my case, said reasonable place was %USERPROFILE%/AppData/Roaming which was an entirely acceptable default.
That is, until several other tools entered the picture and disagreed with Emacs. We've recently switched to using git at work and the git ecosystem needed to have some ideas where its home was. I'm using Git Extensions as the "regular" Windows GUI and TortoiseGit for the Windows Explorer integration, plus the awesome Posh-Git that even made me learn basic PowerShell.
All of this worked fine until I threw magit into the mix. I like being able to interact with the VCS directly from Emacs (who doesn't?) and magit is probably the greatest VCS integration for Emacs. It worked fine as long as I kept the cheat sheet handy, but a colleague of mine pointed out that my magit commits supposedly came from a really funky user that looked very much like the computer guessed my email address rather than the user configured in my git configuration.
Turns out that both git and Emacs respect and look at the HOME environment variable. After settling on a suitable location and adjusting %HOME%, I moved the various dot files into the correct location and can now commit correctly from Emacs with the correct user details. Phew.
Oh, and for those commits that did have the odd username on them, the following commands came in really handy.
To change the author on the current (well, last) commit:
git commit --amend --author="corrected author"
Or if you just want to update the author on the last commit after updating HOME to point at the correct location:
git commit --amend --reset-author