Anger is a tool. We get angry for a reason - it unlocks a reserve of strength that we can't usually call on. That strength comes with a price, but that in the evolutionary context of anger (kill or be killed) that price was always worth it. Think of it like in Anime where the hero uses a special power that can defeat really strong foes, but it leaves them spent and vulnerable.

Unfortunately, in modern day life, the power anger gives us is generally useless, so we are paying the price for nothing.