Again, it's not the slap action, it's the spreading open of the arms to increase the total body surface area over which the force of landing is dissipated, that is the operating principle of a basic breakfall. Slapping -- actively adding force (accelerated mass) to the fall -- is...not...beneficial. Physics is fun, but it doesn't take into consideration the nature of organic tissue and cells, nor the and limitations of organisms under certain stresses within and outside their natural boundaries of stress application.
And, the only "benefit" one is getting from actively making percussive impact of one's limbs against hard objects, whether concrete floors, brick walls, makiwara, or pots of sand, is that you are destroying the nerves in those limbs and thus inurring yourself to pain. That is it. You are not "toughening" or "conditioning" anything.
Is there a doctor in the forum?
Anyone with a biology background besides me, who studied basic physiology, anatomy, vascular tissue/neural generation and all that good stuff? Oi moi moi.