Rage can be a powerful ally. It is anger and raw emotion rolled together to form something that is temporally unbreakable. It will allow you to complete a task that needs to be finished, that you might not otherwise have been able to accomplish.
Rage, however, is a very powerful emotion that will stain your spirit. Left unbalanced, it will consume you, dragging you further down into the darkness until you can no longer see any light.
Remember the first line in the Code of the Gray: There is NO good without evil but evil must not be allowed to flourish. Rage has its purpose but once that purpose is fulfilled it must be silenced.