Anger is not usually a solution, it is a feeling that eats you inside, and holding on to anger is like drinking poison and expecting your enemy to die.
It may come to you for multiple reasons but anger will never repair what was broken.
As Bob Marley said:
If you get down and quarrel everyday, you're saying prayers to the devil, I say."
The feeling of anger is usually an unstable emotion where one loose control over himself. And the use of anger will only lead to pain and destruction.
It is a bad life habit which will push people away from you and can hurt you severely in the long run of life.
But it is possible anger may have its uses... As a mature individual, anger can be a tool. The first use of acceptable anger, is self-defence, if you are attacked and if anger is used against you, being too accepting can lead to continuous mistreatment. And so it is important to show your strength, but remember that anger can be a vicious cycle, an endless chain of revenge which can lead to you digging multiple graves, for your enemy and yourself. More important than anger in this case is forgiveness... To understand and love your enemy is the best way to keep peace around you and within yourself.
Anger can sometimes be necessary in education, for guiding a child or adolescent. Although it is better to inspire and pull people up, there are certain cases where the emotion of anger well timed can be a good kick in the butt which can jump start an individual and push him towards good things.
Aristotle has said:
"Anybody can become angry, that is easy, but to become angry with the right person and to the right degree and at the right time for the right purpose and in the right way, that is not within everybody's power and is not easy."
Yes useful anger is rare, it is not often needed, and may be hard to gauge. What matters to achieve it is to never loose your "control", and to be fully aware of yourself as well as the end goal. To know it, is to be in constant control, to achieve it is to work on your peace, in other words to be angry-well is to "never" resort to anger. To be properly angry is not to never be angry at all.
These words of Yoko Uno can be of help:
"If I am angry I ask myself why I feel that way. And if I can find the source of my anger, I can turn that into something positive."