It provides the freedom to express whatever is bothing you in your own words. It is a positive release of negative energy. This technique work with individuals as well as groups and leads to better mental health. A person doesn't have to a be writer to participate. All you need is a pen and a blank journal.
Metaphor helps to release some of the anger.
For instance, images such as closing the door on the past, pulling the shade between a negative force or person and also walking out into the sunshine of a new day are all useful. This method also works with children, even if they can't write sentences. Their journals can be filled with drawings. They can e xpress their vulnerability through pictures which have meaning to them. They might even print the names of people who have caused their problems.