Not much if a couple of thousand homes in US switches off. There are way more sensitive targets than ”they could randomly hike the electricity usage with 0,0000000000000000001%”

There are always some “stable” power sources kept on standby that can be activated within minutes, for example gas turbines. In European electricity markets, generators can actually be paid simply for keeping this reserve capacity available, even if they are not producing much electricity most of the time.

The problem is that a few minutes is still too slow when a large power source suddenly drops out. The grid needs an immediate response, which can come from fast reserves such as batteries, hydro, pumped storage and other generators that can react automatically.

Pumped storage is basically gravitational energy storage: you pump water uphill when electricity is plentiful, then release it through turbines when power is needed.

I quite fancy electrical grid.