Depression. Nothing good comes out of depression. Not even great art. Maybe valuable human experiences come out of it, but the victim is often too depressed to record or artistically express said experiences.
A little sadness can motivate people to change their lives for the better. Depression will make someone want to do that, but simultaneously kill their motivation and energy to do so.
Most mental problems do have an upside. Maybe they don't outweigh the negatives, but they are there. Depression does not have a single good outcome or side effect. It is utterly useless, it is oblivion's archery skill in the character creation of life, it is the karashian of the human soul, a mental chocolate teapot, the bad AI of the mental disorder Squad based shooter, a completely pointless random excercise in misery that can just decide to claim any person at any time like that annoying friend who turns up at your doorstep, enters without asking, raids your beer stash and "borrows" your copy of the alien quadrilogy.
Fuck depression.