Without power savings feature my box would eat 350 watts from mains and that's a lot of expensive juice going down the gurgler.
Idle/desktop my box is just ~120 watts.
CPU/GPU clock slowdown is an important saver just like TV's eco sensor dimming brightness according to room illumination. It saves me ~100 watt in the evening.
However, all that is not software/driver controlled - it's firmware and it just works! Unfortunately code monkeys writing drivers are unpredictable and nowadays mostly inept to do the job properly even if it works!
Look at Firefox or Thunderbird both are ram guzzler - while I type this in latest FF 296MB ram is taken and this is only a f* primitive browser which should not even use a 100MB for what it is. The email client Thunderbird is taking me 137MB for just sitting there an fetching email from time to time - I would say 20MB would be plenty for such a primitive tool.
Look at Windows the worst offender on this planet - 20GB on disk and 2.8GB in ram here... WHY! I remember times I could load CP/M nicely into 64KB ram and it all worked even the accounting program.
Why is all this? coz coders don't care about ram footprint/optimisation and the compilers are ram guzzler by default settings. The code industry turned into an inept mess of boneheads and we are their beta testers. Hallelujah!
Okay, just my 2cents and now gunna go breakfast is on the table!
just another observation...
happy Saint Nicholas Day (okay we're 1 day ahead!)