If you look on Google, you will find people talking about how to take a punch (roll with the blow, relax, etc.) But does this really matter? If you get punched, then all that kinetic energy is absorbed into your body, whether you know technique or not. Thus, assuming an opponent is not using a gun or knife, could you just rush forward and attack the guy and win? After all, even a baby absorbs kinetic energy.
Yes, it matters.
If you roll with a punch, you absorb less kinetic energy from the punch than if you stand still and receive the blow. When you reduce the speed differential at impact, you reduce the kinetic energy transfered upon the collision.
Where you absorb the kinetic energy matters too. If someone punches you in the solar plexus, this impairs your breathing. If someone punches you in the arm, it just hurts.