Can being angry have positive consequences?
Yes, if the anger is short-lived and is a call to action to right a wrong. My worry, as spelled out in the book, Forgiveness Therapy, with Dr. Fitzgibbons, is anger that becomes prolonged (months or years) and intense. This can lead to a host of psychological compromises. We need to make the distinction between healthy and unhealthy anger.
For additional information, see How do I know if my anger is healthy or unhealthy?