Smaller electronics in the chips means they use less power and thus produce less heat, or alternatively, Apple can dial up the speed more, when switching from 5nm chips to 3nm chips. It is not going to make them 200% faster, but the jump from M2 to M3 is thus likely significantly larger than the one from M1 to M2.
We want as fast computers, that use as little power as possible, and therefor the prospect of 3nm chips is exciting. But if you need a machine now, don't wait, just buy, they are already very fast and energy efficient, now we have moved away from Intel chips. But this is summer 2023 at the earliest, and Pro and Max M3 chips fall 2023 at the earliest, and possibly first spring 2024.