Siljo3

Hello, I bought Yamaha YZ250F 2017. I have one question. I know that Starter knob/idle screw is for starting a cold bike, but when I put it back on original position and if I turn it clockwise, the motorbike stop running.In manual doesnt write anything about turning the knob, only to pull it out for cold machine and put it in again when is warm. And on knob is written "open" if you turn it anticlockwise. Can someone explain me what turning this button do? Can I have impact maybe on how much air runs into machine or something like that? Thank you and best regards, Matevz