It seemed like a gimmick. Beijing has hordes of scooter-riding delivery people to fetch your noodles and dumplings at the swipe of a smartphone app. I gave the robots a try anyway, placing my salad order on a delivery app as usual, but specifying that I wanted a robot in the building to bring it to me. The advantages soon became clear. They don't get impatient or angry, like human delivery people sometimes do, and they don't waste my time asking for directions.