The stored enegry is proportional to the square of the rpm, so a 3% increase in rpm is actually a 6% increase in energy. It is not enormous, but it truly helps in Cat A and H-V engine cuts. For a hover cut, rotor energy is worth about 1/3 of the means to land, and engine power is worth about 2/3. So if we make a 6% increase on the 1/3, that would help increase Cat A weight by perhaps 2% total. For a 6000 lb machine, that is 120 lbs.
I think 212man has it right.