I have been journaling for years and find the records very useful for later review, particularly when putting history together for a new pdoc or T.
Sometimes I have so much to write down, but more often my memory lets me down and I can't piece the thoughts together.
Sometimes I find writing and thinking about issues very stressful, and I keep the content to a minimum.
Then there is the mood diary that I keep, where I log the meds I use, how much sleep I had, manic-depression scale, etc. The mood diary is easier to keep going every day because I don't have to go into some of the stressful thoughts again.