Case by case thing for sure. If I was calling for a harm move, though, I wouldn't outline the results of the harm until that was completed. So I might say "You take 1-harm. It’ll bruise but whatever," but then I wouldn't call for a harm move. Or, I might ask the player to roll for harm, saying, "alright, so you take 1-harm, roll the harm move," and then narrating the results based on the roll, like, "shit, you thought it was just scrapes, but this one's actually pretty deep and still bleeding" (+1 harm) or "it's just 1-harm, but you know how you've only had one real meal in the last three days? Even that light blow is enough to make you light-headed at this point. Your vision swims and you're not going to be any use to anyone for a couple minutes here" (out of the action).
Basically, you just can't describe the outcome of the move before you actually make it, same as any other move.