If you listen to the whole thing, I think it becomes pretty obvious why they record it. They're just constantly riffing ideas, constantly. Then this will happen

If you listen to the whole thing, I think it becomes pretty obvious why they record it. They're just constantly riffing ideas, constantly. Then this will happen, no then this, yeah and then this, etc etc. I would never trust a normal assistant to "keep notes" that are usable for something like this. A recording would seem to be mandatory in order to revisit ideas.