In popular mechanics, a "useless machine" is one that does nothing beyond turning itself off again. When made in LEGO, you will often find them powered by a motor, by gravity, or by some other means. When I saw the new wind up motor in the LEGO Technic sets 42033 and 42034, I knew it could be used to power a "useless machine".
The only disadvantage of using a wind up motor, is that it runs very fast. It easily reaches a high speed, as long as the friction is low. To overcome this problem, I put a clockwork escapement mechanism into the machine, to limit the speed of the motor when the device is running. Here is the result: