Sometimes, I just need to get my thoughts out on paper before I organize it, and express my thoughts in their true, unadulterated form. This requires the release of writing sans any real form or organization. This pretty much equals really, really bad writing.
It's even fun to write poorly. It's like throwing paint against a wall. You don't worry about the consequences or how messy it is, but all you have to focus on is the release of throwing it. Then, afterwards, you can look and see what patterns formed on said walls. It doesn't have to be that chaotic, though. Sometimes, it's more like tinkering with words, playing with different forms. It can be really cool or I could make an awful concoction.
Not all of my first drafts are even bad, though. Most of them just could be better. Every once in a while, though, I get a real turd of a writing and sometimes, no amount of revision can fix it. Sometimes, my piece doesn't get better after a revision. My second drafts can be equally as bad as my first drafts. At that point, I usually give up because I figure that I either need time away from the piece or that it's just time to throw in the towel and move on.
Poorly written pieces often force me to think about why the piece was bad and how I can improve the next one. They force me to examine my writing more. It also gives me something to compare my better writing too. Sometimes, if the idea is good and the writing is bad, it helps me come one step closer to refining the piece.
It also helps me outside of my writing. It gives me the permission to be human. Not all of my pieces can be wonderful after all. These bad pieces teach me some humility, which is especially useful if I've been coming out with a lot of really good ones.
Giving yourself the permission to write poorly as a writer is so important. Not everything you write can be a masterpiece. Even the best of writers produce these every once in a while. We might as well make use of them