[userbinator]

The difference between idle and full power is very large in modern CPUs - a typical laptop one can consume an average of a few watts at idle, but several dozen at full load; furthermore, they can switch between these states thousands of times per second. This is why CPU power circuitry is not easy to design, since it has to keep up with the very fast changes in current as the CPU transitions between power states.

Incidentally, this is also why you may be able to hear audible sounds from a computer when it's idle or running some particular process - the wakeups/sleeps are happening at a frequency in the hearing range, and the components like capacitors and coils can act as tiny speakers.