From what I understand, Git doesn't really need to track file rename/move/copy operations, so what's the real purpose of git mv? The man page isn't particularly descriptive...

Is it obsolete? Is it an internal command, not meant to be used by regular users?

git mv oldname newname

is just shorthand for:

mv oldname newname
git add newname
git rm oldname

i.e. it updates the index for both old and new paths automatically.