What task does your computer perform to consume 4.2ghz?
Load. Any load. If its idle, and I were to say open a web browser. Or any program. It will hit its max speed instantly but only for a few ms. So everything it does happens fast. As soon as theres no real cpu load it drops back to under 1ghz.
If you hav a CPU like the new one in my desktop PC it has 16 cores, 32 threads. Any single core, or more than one core, up to as many as required can boost
individually to run whatever load or thread is needed.
So at any one time there will be 16 cores all at different speeds from idle (and very low power saving you £££, and making very little in the way of heat) up to all cores maxed out at 100% which is around 250 watts of £££ and heat to dump. That seldom happens in any desktop computer though. Unless you are doing realyl heavy 3d solid editing for a cnc machine ir something similar, or 4 and 8k movie editing. And then you really need a GOOD 3080Ti to 3090 graphics card to help too. And thats another 270 to 360 watts of heat... And 1500+ £££.