As was mentioned above, that star thumb wheel throttle brake is a hold-over from days with carbs on the engine. It would allow the rider to fire up the bike using the enricher, and then "freeze" the throttle at some rpm (like between 1,200 and 1,500) and close the enricher but still let the engine warm up enough before taking off. This is important in the EVOs to extend the life of the base gaskets.
But remember, there are NO safety controls when the throttle is mechanically set in any particular position. So if an emergency happens (like a flat, something in the road, other traffic braking quickly, or worse) when the throttle is braked at a particular setting, YOU have to release the throttle brake. IMHO, this is a very dangerous practice.
TQ