In name, we only have one-step sparring, at least at my level. However, most of the black belt "one-step sparring" drills really require multiple steps, from both people involved. In fact, the only one that doesn't is one that used to have more steps but was simplified.
Do I think I would ever use any of these drills exactly in a fight? No, but that's not really their purpose. They teach basic applications of some sections from the pyung ahn forms, which give you a lot of practice using some things you could definitely use in a fight, if not in that exact sequence. They also teach reaction, distance, and control, allowing you to focus on a target, rather than thin air, as well as giving you a controlled situation in which to practice, so that you can focus on improving specific moves, which is limited in sparring (although I certainly don't want to seem like I'm belittling sparring practice).