Do you notice a theme here? Creativity and expression are the two most important things to me, so journaling is also a big part of this. I feel like my purpose and feelings about journaling are pretty similar to poetry, so I will make this one pretty brief.
Since my mind can be an unstable place and has been for a long time, it helps me put words to feelings and cope with those feelings and happenings in my life. Plus, it is nice to write without any need for perfection (even if it arises within myself sometimes) and let the stream of consciousness take over. The word for this experience: freeing.