Re: [FIXED PATCH] Make rebase save ORIG_HEAD if changing current branch

Brian Gernhardt [off-list ref] writes:

My final thought is that the rational ORIG_HEAD and when we set it is
not clearly documented anywhere.  But I am currently out of time to
work on git, so that patch won't be coming from me soon.

The idea behind ORIG_HEAD is to have an anchoring point before an
operation that moves your HEAD in a drastic way.  Think if it as a
poor-man's reflog -- in fact it predates reflog.

That is why reset saves away the HEAD before it does its thing, so that
you can easily say "Oops, I did not mean it -- reset ORIG_HEAD" to flip
back to the previous state.  Both a fast-forward merge and a real merge
can be undone by resetting back to ORIG_HEAD.

So in that sense:

 (1) ORIG_HEAD is not strictly necessary these days, because we have
     reflogs;

 (2) Even then, it is handy and useful, and we could add ORIG_HEAD to more
     commands such as "git am" and "git rebase".