I personally found it very destructive and made me a lot worse, so I stopped doing it. Not only for the reasons already given above but because the depths of my anguish were there in writing as a reminder of how ill I was. I hated having it in the house, even though I hid it. Eventually I destroyed it and stopped keeping one. I find creative writing a lot more helpful. But that's just my experience, you may find it different. Good luck, whatever you decide.