my take on "slapping the mat" is that it is not an attack , never attack the ground it is much bigger than you are. but rather it is that your arms slap the floor as you land. as such they increase the surface area of your body in contact with the floor and so distribute the force of contact over a wider area. the slight tension in the muscles required for the slap makes the body react more like single rubber block and less like damp spaghetti, more bounce, less splat. it also redirects the force of hitting the ground away from the spine / head and towards the shoulders and arms. better a broken shoulder than a fractured skull.