Destroying the enemy may seem the obvious goal. But capture may result in later wars. Glory may seem to be only found in battle. The enemy seen as evil deserves to be punished severely.
Yet this is not the best way. Harming people when it is not necessary creates enduring enmity. On the other hand, showing superiority without fighting invokes awe.
A captured force has to give up its weapons. It may be used in negotiations. Through treating them with respect you may draw the sting of their anger against you.
In business, it is better to weaken and acquire competitors or go around them, rather than waging expensive competitive battles. When you are seen as superior, you may be able to induce their better people to join you, weakening them further.