I think it could make sense if they start with a hard requirement that it must be able to do a good job of cleaning a not-yet-mapped house. (They might feel that is important for making a good first impression or avoiding user confusion.)

If they manage to solve that case, then the benefit of retaining the map is less compelling. By definition, you can do an adequate job without it. So then it's a question of what you gain in cleaning performance/efficiency vs. the extra complexity and any potential problems it might bring.