The fan is the most notable difference between Apple’s two new laptops based on its own custom M1 chip: the new Air, which does not have a fan, has to throttle performance as temperatures rise. The Pro can just turn on the fan, which means it can sustain performance for a much longer period of time.
Sure, there are some other small differences: the Pro has a slightly better display and better mics and louder speakers. It has a bigger battery and thus, slightly longer battery life. And yes, it has the hopelessly confused Touch Bar instead of a function row on the keyboard. But in terms of performance, it is essentially the same as the Air unless you push it for long periods of time. And that all comes down to the fan.