The reverse is also true; “writing as therapy” or “writing for therapy.” that’s the main reason why I write fiction (though nothing has been published, yet, and may never be,) to dump traumas and “certain life events” into a fictional work and this helps me to work out stuff.
I like to turn people who have done me wrong into novel characters and have them bleed a little. (Just a little. Juuuuuuust a little.)
(It is therapeutic, in a way.) 
P.S. No need to freak out (although I’m far from being the only one doing this), I do the opposite too.
I think the therapy value lies in the trauma (or whatever) is no longer internalized but is objectified; it’s “out there” and someone else, even if only a fictional character, is dealing with it. How we, as the writer of the work handles the problem, helps with the therapy. It’s like we are “helping someone else” deal with the problem, and maybe get the help we didn’t.
It beats paying a shrink or sitting in AA rooms.
It sure helps with moving on.
Whatever it is, it is always less weight to carry once on paper.
And for the positive things, you just so happen to make them eternal.
. . . . .
Better than doing it in real life.
I became aware of bibliotherapy during a radio interview with a musician. (Don’t remember now who it was but Bill Bruford the drummer comes to mind.) He mentioned that he practiced and benefitted from it. It is also implicit in the dialogue between Joe Fox (Tom Hanks) and Kathleen Kelly (Meg Ryan) in her bookshop.
Bibliotherapy has been practiced for a long time by people who got solace and guidance from reading texts such as the Bible or Bhagavad-gita.
“In the morning I bathe my intellect in the stupendous and cosmogonal philosophy of the Bhagavad-gita, in comparison with which our modern world and its literature seem puny and trivial.” Henry David Thoreau
“I owed a magnificent day to the Bhagavad-gita. It was the first of books; it was as if an empire spoke to us, nothing small or unworthy, but large, serene, consistent, the voice of an old intelligence which in another age and climate had pondered and thus disposed of the same questions which exercise us.” Ralph Waldo Emerson
“When doubts haunt me, when disappointments stare me in the face, and I see not one ray of hope on the horizon, I turn to Bhagavad-gita and find a verse to comfort me; and I immediately begin to smile in the midst of overwhelming sorrow. Those who meditate on the Gita will derive fresh joy and new meanings from it every day.” Mahatma Gandhi