Comment by duskdozer

I don't think I really understand the way jujutsu is doing this, but if it's what I think, one example would be that you realize while working that some changeset is getting too big and makes sense to split it. So B would depend on A and be on top eventually, but you don't know the final form of B until you've finished with both. I've always just done this with rebasing and fixups, but I could see it being easier if you could skip that intermediate step.