U punch (yama zuki) found in bassai Dai.
could be breaking past your opponents oncoming hands in order to grab you at the chest or grapple - then apply the head charge forward, so using the head as application within the kata - also teaches you to be aware of the head but attack yourself!
or - imagine you are in a head lock (rear) so you would be in a low position (check stance within kata - zenkutsu Dachi) then mountain punch - one hand to give you breathing space or grab certain vital areas!! or pinch the femoral artery and the high punch to attack the back of the head - GB20! (which they don't see coming)
then coming back up from the u punch could be drawing the head back and giving you control...
just another application to add to the list.
Charlie.
www.lonepineryu.co.uk