i've tried it on my sct tune bird. with the spout in, standing still and punch the gas the tire roasted for couple seconds. took it out, it roasted the tires for about 1 second and no more.
with the spout out it retarded the timing by couple degrees.
this is useful if you got bad gas and the car is pinging. take it out and it may reduce or eliminate the pinging thus save your engine.