From my exercises with the revert command I made the observation that the abort option works very similar to the one of the rebase command in that it tries to reconstruct the pre-operational state of the current branch.
You're on the right track:
git revert --abort rolls the sequencer state back, so the workspace and history end up as they were before the start of git revert; git revert --quit only removes the sequencer state, so the workspace and history remain as they are (with a partial revert in progress but forgotten about).
From my quick experimentation, if a revert needs manual intervention, git revert --quit only forgets the previous commits; REVERT_HEAD remains in place so you still need to --continue or --abort. The latter keeps the forgotten commits as a result of the --quit.
As far as use cases go, I've never needed to use --quit, but I'd imagine if you're part-way through a revert and decide you're not going to need the remaining reverts, but you do want to keep those you've committed so far, then it might come in handy...