There is more butane on the higher grades (lowers the flame-speed and therefore raises the "octane" rating. "Octane" is not an actual substance, it is only a "rating" of resistance to pre-ignition.
Higher "octane" rated fuel burns SLOWER, and is harder to ignite. This is why it reduces "knocking"
The hot carbon deposits have a harder time igniting it, the compression heat has aharder time igniting it. And when the spark plug does ignite it, it burns SLOWER, so it doesen't smack the piston so hard at the wrong time... reducing pinging or knocking o pre-ignition.
Most RoadStars do not have high enough compression ratios to need premium fuel. But my own experience has shown that on REALLY HOT days, some engines will run a little better on premium, due to the extreme heat that might cause them to "knock" around town in heavy traffic.
Premuium fuel contains more "butane" which atomizes a bit better, and burns a bit slower.
If you use premuim fuel and you don't need it, you are wasting your money.
If you find it makes your engine run better in hot weather with less knocking, you are not going to hurt the engine by using it. Knocking, or pre-ignition is pretty hard on the rings and pistons if it is severe enough.
I think most "carbon problems" come from running too rich, running too cold,
and "LUGGING" anngine under heavy load. Lugging is probably worst next to running too rich.
(In lugging, the flame gets snuffed before it gets everything burned.)
I can usually use regular most of the time, but on really hot days I will stick to mid-grade or higher.
That's just what I find works good for me. But I'm very careful with my bike, and how I run it.
Gasolines are not all the same as brands differ. And you have to know the difference between "pump octane" and "research octane" ratings. If gasoline is more than 30 days old, it's "octane" rating declines rapidly, as the butane escapes and the gasoline deteriorates. In some cases I can see some people having to use higher grades to compensate for many factors that are beyond.
Ever since they took the lead out of gas, we've had poor "octane" ratings and gas that spoils rapidly.
That's why avaitaion-gas still has lead in it. Aircraft gasloine engine technology hasn't changed much in the last 50 years to allow unleaded, poorly graded fuels to be used. There's too many risk factors involved when you change something that works, and is tried, tue, and proven to be reliable for safety.