Closing the flapper stops the water in the tank from going into the bowl.
This is completely unnecessary IMO. You stop the water in the tank from going into the bowl by not continuing to flush a clearly clogged toilet. There’s no issue with the flapper in this scenario and it will automatically seal in a few seconds from water pressure.
Turning off the water will stop the tank from refilling. Closing the flapper stops the water in the tank from going into the bowl.
I would imagine most people aren’t fast enough on the draw to think about doing this first step.
This is completely unnecessary IMO. You stop the water in the tank from going into the bowl by not continuing to flush a clearly clogged toilet. There’s no issue with the flapper in this scenario and it will automatically seal in a few seconds from water pressure.