CPU's only really consume most power when they are processing data and full tilt 100% per core. When idle they go into a lesser power consumption state even if overclocked. Intel CPUs have Speed Stepping which when the CPU is idle unless Stepping is disabled somewheres it will generally come to rest at around 1/4 or 1/5 clock, so if your CPU was idle and utilizing Speed Stepping, it will be around 1/4 or 1/5 the clock of full clock of 4.5Ghz and will be somewhere around 1.12Ghz or 900Mhz. AMD also has this stepping feature but they call it Cool n Quiet the fan speed can be reduced lessening noise and the CPU clock drops down by quarter clock intervals such as my 2.8Ghz idles at around 700Mhz saving electricity and not creating unnecessary heat.
https://en.wikipedia.org/wiki/SpeedStepThere really is not much benefit at all to having this feature disabled to have it running full clock all the time. The CPU is able to split second change from say 900Mhz to 4.5Ghz without missing a beat, and if you ran a test to see if there is any performance loss in doing this, it would be a very very small difference that is unnoticeable to the end user. The only benefit I can think of to forcing a CPU to stay full clock would be if the program itself didnt stress and load down the CPU enough to have to ramp up to full or max clock, and so it could slow that single threaded program possibly by calculations that happen at slower clock. 99.9% of the people out there would never run into this as well as if performing scientific calculations, usually the CPU is loaded down pretty well for all cores to make full use of the multiple core CPU's potential vs say only using 1/4th of an AMD Quadcore etc.
There are tools out there to monitor the systems GPU and CPU speeds. You can watch the clocks go to maximum speed and go back to an idle at 1/4 or 1/5 clocks or if there is something going on in background to where its not completely idle 3/4, 1/2, or 1/3 clock etc.
