It just stays in the lower gear longer so it stays In the powerband rather than shifting all the time. The limiter is set at one place, it just revs higher in each gear before it will shift up.

 

Power button does nothing at full throttle, power button increases your shift RPM AT PART THROTTLE, now if you are off the throttle coasting at 40mph and you floor it the power button on will down shift quicker and reduce the delay, but from a dead stop and flooring it and not letting off the gas there is no difference between power button on or off.