To me, the difference between the colloquial term “brainstorming” and this site’s term “babble and prune” is the intentional choice to split the activity into two phases: an unfiltered idea generation phase followed by a filtering/editing phase. Emphasis on “unfiltered”, for the anxiety-reducing and writer’s block circumventing reasons you gave.
I’d be grateful for an update down the line, if you come across any unexpected benefits/shortcomings.
nit:
I think you meant “no non-black ravens” here.