At the 3rd National Aikido Seminar in Melaka 7/11/09 and 8/11/09
I noticed many students habitually slapped with great gusto on the mat without regard to the health of their limbs. It is as if banging forcefully on the mat is the only acceptable way of taking ukemi. If the floor had been concrete instead of tatami mat slapping forcefully on the hard and unyielding surface will surely damage the limbs in the long term. Even one sensei opined that by banging hard and loud on the floor it would impress the public with the power of Aikido while falling and rolling softly and quietly would make Aikido appear as dull and uninspiring.
In Semenyih dojo where the trainees practice on a hard concrete surface with no mats, such reckless floor slapping antics are actively discouraged. Instead the trainees are taught how to relax and soften their bodies so as to resolve the impact of bodies crashing on the floor. In addition the trainees are also taught how to exhale just before hitting the fall. In my experience slapping is probably safe if you are in the prime of your youth but as you grow older continuous slapping the floor can lead to bone and tissue damage.