The "dingdong hole" as I like to call it, is useful when you're wearing pants with a belt and you don't want to undo your belt. Undo the pants zipper, grab your unit through the hole and go to town.
I thought that only for when u want a quick fuck/clothes ons sex & cant be bothered to take off ur pants or maybe u may take off ur clothes an only leave the boxers as ur too shy to go full nude.