Computers come with default settings tuned towards conserving electricity, and this needs to be changed by gamers to acheive maximal performance. These settings are found not only in the operating system and GPU control panels, but also the BIOS. One such setting is called "C states" in the power settings of intel CPUs. Essentially what the feature does is to degrade CPU perfomance to save power. By switching it off, my i7-8700 went from 190-210 FPS to 200-220 FPS, as demonstrated in this video: Of course this is only beneficial if the computer is CPU bound, i.e. the GPU is not the bottleneck.
The various C States allow power saving measures only when the CPU is idle - technically it shouldn't make any difference if the CPU is 100%. However some of the C states have a little lag when shifting from low to high power and this can cause a very slight performance degradation. BUT disabling the deeper C States means that the CPU is 100% Voltage and frequency ALL THE TIME (as long as the cooler is good otherwise you run the risk of thermal throttling). So for a very minor increase in performance you are paying a hefty price in terms of thermals and electricity. Also worth noting that the more modern processors use additional methods for controlling power draw - allowing short bursts of frankly alarming power consumption to do all-core boosts (i'm looking at you Intel). I'm not even sure what happens to these when the C States are limited - but would not recommend it based on the fact that they run extremely hot when maxed. So - disable if you like - but understand the consequences.
What limits a default i7-8700 is power throttling, it maxes out at 65W and auto-adjusts the frequency accordingly. This 65W limit can be changed with Intel XTU but then a better fan/cooling is necessary. By only disabling C states, there is no difference in thermals or electricity, simply because the CPU is constantly throttled at 65W while the game is running, regardless of C states being on or off. From two 20 minutes test runs confirming this, it actually looks like there might be a slight improvement with C states disabled.
I wasn't talking about while the game was running - rather - when the game is not running ! If the C States are disabled, how much juice is being used ? If the CPU can't go into a deeper level of sleep - more electricity will be used than need be. BUT it's your choice and cash at the end of the day (assuming you pay the bills !) and if you're happy with the results then great.