By 1918 a Clerget handbook advised maintaining all necessary control by using the fuel and air controls, and starting and stopping the engine by turning the fuel on and off. The recommended landing procedure involved shutting off the fuel using the fuel lever, while leaving the blip switch on. The windmilling propeller made the engine continue to spin without delivering any power as the aircraft descended. It was important to leave the ignition on to allow the spark plugs to continue to spark and keep them from oiling up, so that the engine could (if all went well) be restarted simply by re-opening the fuel valve. Pilots were advised to not use an ignition cut out switch, as it would eventually damage the engine.
That sums it up nicely. It was essential to have power and the only way was with the 'blip' switch. It is worth noting that the Clerget had a life of only about 50 hours - but it depends on what was 'using' it.
On the Shuttelworth aircraft, as it was on approach, the blue smoke points directly to 'blipping' just as it should - but sadly the port wheel struck the top of a post as I saw it. The rest was almost inevitable due to weight and forward speed. The reason will be heard in due time.
As always, it is good to hear the pilot was OK.