I have no idea how CPUs work, but MCUs do sorta work like how they describe; want to save power? You can easily tell the chip to cut power/clock to certain peripherals, change stuff like core clock speed and memory access latencies, make some peripherals run at lower or higher clock speeds than the core, etc etc.

You get really fine-grained control that allows a powerful and beefy chip to achieve really good power efficiency if the application is well-written, and a sleek ultralight 1.8V chip to devour power if it isn't.