In today's times, it is not necessary to practice the antique art of hand and foot conditioning in which you would intentionally try to harden the knuckles, palms, heels and balls of the feet. The reason it has been practiced for years is that in ancient times, it was necessary to desensitize the hands and feet to be able to strike through armor when necessary (think Samurai armor for example).
However, times are now different.
In today's sport competition, strikes are either forbidden (examples include judo and submission wrestling) or pads are worn (sport karate competitions for example). Any time has been spent on hand and/or conditioning would be nullified since those areas would be covered.
In practical self-defense, conditioned hands and feet can give lawyers a field day in the courtroom. It may be pretty hard convincing a judge and jury that you haven't been preparing for fighting instead of defending yourself.
Also, with an understanding of appropriate target areas on the body, you can easily avoid striking bony areas that would normally damage an unconditioned hand, or if you do strike a bony area, you can do so with an appropriate strike that will damage the opponent instead of yourself. As the old maxim goes, strike a soft part of the body with a hard part of your body and vice versa. For example, a fist to the forehead can potentially break your hand, but a hammer fist to the bridge of the nose would work wonders. In my next few posts, I will discuss some of those target areas on the body.
Another potential problem with conditioning is the likelihood of doing permanent damage, especially with the hands. Anyone that uses their hands to perform intricate skills for a living (surgeons, musicians, massage therapists, etc.) would definitely have issues with hand conditioning.