This advice completely ignores the facts. First, many engines will sputter and die before the fuel level drops below the idle jet. Just the way engines are. Second, even after the fuel level goes below the idle jet, and the engine has stopped, there are two things still happening that defeat the purpose of this technique. One, there is still fuel on the float bowl whose presence will affect the jets. Any mechanic knows this. And two, there is still fuel on the circuits, that is, the jets and passages, the jets due to capillary effect and the passages due to the vagaries of how carburetors are cast, with many blind holes, sharp corners, and other characteristics. See my video on this.