On mine, "On" closes the valves, making it just slightly quieter. I never close them and I believe that leaving them on (closed) one time was the cause of a battery drain I had. I've not had the problem again by leaving them off (open).

That beind said, OMG! I've got about 3.5k miles on my GT version QuickSilver Titan, and I swear it just keeps sounding better and better. Is this possible? It is the perfect loudness for me without the valves, and it's not rowdy when pulling into the neighborhood. 4krpm is harmonious, and up around 9krpm it screams like an F1! I don't know what engineering went into these, but kudos!