~20% is residential—still significant. Plus ~30% transportation, which as we transition to EVs become more and more relevant to residential energy use.

But even commercial and industrial could be optimized in the same manner. I've been thinking: If electricity is much cheaper during certain periods, would factories be built to only run during those times?

https://www.eia.gov/energyexplained/use-of-energy/

This is already a thing, but it‘s only done at “enterprise scale”. Meaning account managers meet with energy purchasers at large manufacturing plants to negotiate “interruptible supply” contracts. The notice periods, levels and tariffs are all negotiated individually. “Pricing managers” on both sides of the negotiation spend a long time modelling the deals in Excel. If algorithms could replace the pricing managers that would save both sides some time and money though, not to mention making it available to the residential and SME market.

If you're in the UK, then Octopus Agile tariff gives you a variable price and an API with IFTTT integration so that you can switch devices on and off depending upon the current price: https://octopus.energy/agile/

That's really cool, for all the spam/ads I have seen about Octopus I've never seen this before, and this is the first time I'm interested. (Ordinarily I'm only interested in price, viewing it as a straightforward commodity, and Octopus has never been appealing on that ground.)

This is already a thing in Australia

Just because something isn't "environmentally important" (whatever that means) doesn't mean you can't optimize it. We need to shift into the mentality of thinking about the environment. Don't slap the hand that's interested in making a difference.

You can optimize small things, but it will only have a small effect.

Better than nothing, sure, but the danger is that you only deal with the small things because you're not even aware of the big ones.