No, is not a command it is a negative marker, just like yes is a positive marker during training. The disobedience is marked and the dog is removed from the couch. If you say off, and the dog obeys and you praise the dog, you have praised the dog for getting off the couch. So getting off the couch is a fun/happy thing to do, so this will not discourage the dog from getting on the couch again and you have diverted away from the issue which is being on the couch in the first place.
IMO disobedience should not be corrected with another command, the original fault must be corrected first.