The only time I see a rebase fail is due to a conflict. Which can be aborted with git rebase --abort no need for reflogs unless you really mess things up.
Not sure I would say that is a rebase failing - just you messing things up. Can happen with any merge. But yeah that is a place where reflog would be useful. But I dont see why it would be on the cheat sheet instead of a git rebase --abort or be rebase specific.
It can be nice when you successfully do a rebase (after resolving conflicts), but change your mind about the resolution and want to redo it.
Doesn't come up that much, but it's been handy once or twice, for me. It's also just nice security: no matter how I edit commits, I can always go back if I need to.