[Bartweiss]

This is a much better expression of what's great about chalkboards than just the order of steps, thank you. It's not so much seeing a problem worked out in sequence as seeing it worked out for real. Even if the professor is working from lecture notes with all the steps, writing them out live engages with the content in a way that pressing "next bullet" doesn't. And as you said, what's missing is the messiness - catching mistakes in the notes, making mistakes on the board and finding them, puzzling over what belonged at a missing step.

Everyone jokes about the frustration of copying a full blackboard worth of notes and then having the professor go "wait no, that wasn't right" (myself included) but it's a valuable experience. That moment of "hm, hold on a second" is where the math is happening, and a chalkboard helps professors and students notice that. (And of course, when something "isn't quite right" on the Powerpoint, it's a tremendous pain to fix...)