> CPUs mostly run idle. Even if you had a theoretical CPU using zero energy, most people are not going to get 30% battery life gains

I don't agree. Simply disabling Turbo Boost on MBP16 nets me around 10-15% more battery life. Underclocking a CPU can even result in twice to thrice the battery life on a gaming laptop under same workload.

Here's more details. https://www.extremetech.com/computing/304884-disabling-intel...