We generally consider something beneficial if it promotes happiness. But when we ask ourselves, "Am I happy when I'm angry?" the answer is undoubtedly no. We may feel a surge of physical energy due to physiological reasons, but emotionally we feel miserable. Thus, from our own experience, we can see that anger does not promote happiness.
In addition, we don't communicate well when we're angry. We may speak loudly as if the other person were hard of hearing or repeat what we say as if he had a bad memory, but this is not communication. Good communication involves expressing ourselves in a way that the other person understands. It is not simply dumping our feelings on the other. Good communication also includes expressing our feelings and thoughts with words, gestures, and examples that make sense to the other person. Under the sway of anger, however, we neither express ourselves as calmly nor think as clearly as usual.
Under the influence of anger, we also say and do things that we later regret. Years of trust built with great effort can be quickly damaged by a few moments of uncontrolled anger. If we could tame our anger, such painful consequences could be avoided."
~ Thubten Chodron from "Working with anger"