Worthwhile if you anticipate something going wrong, but usually things are just fine or a `git rebase --abort` will get you back to a safe place (if you are using an interactive rebase).
> HEAD names the commit on which you based the changes in the working tree. FETCH_HEAD records the branch which you fetched from a remote repository with your last git fetch invocation. ORIG_HEAD is created by commands that move your HEAD in a drastic way, to record the position of the HEAD before their operation, so that you can easily change the tip of the branch back to the state before you ran them.
