in the link plus manual it described it as setting the butterfly open a certain amount and letting the engine idle high and the air flowing through and it would fuel cut (if i understood it correctly) to keep the engine from going any higher in the rpms to keep manifold pressure at 0psi

 

it is used to boost the turbo quikly. by letting more fuel thru the exhuast.
it is not permanantly on., you can switch it.