Significant. The Steam Deck’s APU is 15W max. Just a desktop CPU is usually at least 65W, but some can draw 250W+ at the high end, and a dedicated GPU is anywhere from usually around 100W to even as high as 400W. Now, granted, desktop CPUs and GPUs can certainly run in more efficient power states than that, but it’s still pretty night and day overall.

Of course, all that extra power gives you a huge boost in performance, so it’s not a apples to apples comparison. That extra performance doesn’t scale linearly, though, so things get more inefficient the more power you’re pushing though it.

Devices intended to run from a battery will always be much more power optimized than their plug-in brethren, and the Deck is no exception. You do, of course, pay the price in terms of perfmance, as it’s a trade-off.