My guess is if you changed your coolant every year, there would be little if any need to flush. Good Point.
My bike is used and I do not know the last time the coolant was changed.
I flushed with water as I am a cheap Bas@#$ and did not want to flush it with costly coolant.
I also followed Fred's DVD on coolant replacement and he flushed the system a few times. (I think he used 50/50 mix to flush)
FYI. I bottled my old coolant and flush to recycle and to keep it away from the Dog. (CA frowns on dumping coolant in the storm drain). I did find a lot of white colored sand grain sized particles in the old coolant and water flush. So for my 2008 with under 9000 miles some scaling was in the fluid.
per service manual
Cooling System Flushing
Over a period of time, the cooling system accumulates
rust, scale, and lime in the water jacket and radiator. When
this accumulation is suspected or observed, flush the cooling
system. If this accumulation is not removed, it will clog
up the water passage and considerable reduce the efficiency
of the cooling system.