The practice of tameshiwari is a very effective method of increasing striking power. Without the ability to deliver maximum damage in an attack, much of the usefulness of a striking system is lost. Those who underrate the importance of power find themselves extremely susceptible to being tackled. Imagine yourself firing a gun at a charging attacker, only to realize that the clip is empty. At this point it is too late to rework your game plan. If you have never questioned or tested the effectiveness of your strikes, you probably do not have any backup because you never thought you would need an alternative.
Striking is the first range of combat, so it is a shame to waste it by skipping directly to grappling. It is also more than simply a method of distraction before the fight goes to the ground. In order to finish a fight on the feet, your strikes must be executed with maximum effect. That means you need damaging force. In order to use force without sustaining injury to yourself, you must have conditioning.