Have you ever been working on a player's forehand and thought "they're just not getting it". And instead of talking the player's ear off with detailed mechanics or trying every cue in the book, you decide to get them to throw a med ball.
All of a sudden, after just 1 or 2 cues - something like “thrust your rear hip” or “turn your torso, then release the ball” - they found the correct movement. You then return to hitting forehands and voila, they finally ‘get it’.