What has journaling done for you, that couldn't be done with honest, and regular self-reflection?
This is an important point.
I noticed that people have a serious lack of awareness in how significantly their thoughts/actions "drift", with respect to how they relate to a plan/belief/idea. In the short term, its indistinguishable from being intentional. In the long term, you're wondering how you ended up so far from what you had originally planned or believed (and that's if you even have the awareness to notice the change).
This seems to primarily occur with those "mirco" thoughts and patterns; interestingly enough, these are the ones which are most susceptible to being influenced by our emotional state.
An outlet for the unfiltered stream of consciousness is important. You just write whatever comes up. No-one else is to read it. That's equally important.
As a result, I'm happier and more creative. But if you want to start, I wouldn't advise focussing on the benefits too much. In all likelihood, you'll start because you need to, or because the time is right. Hope that helps!
This summer I’ve been kind of depressed being unemployed and haven’t done it but it probably would have helped.
I try to journal every day and have been since around 2014. The main "benefit" is the ability to look at a random date (say, Jan 19th 2015) and know what I was up to that day/period.
I started journaling hoping it would help clarify my thoughts/reveal something dormant in my mind. It did neither.
One odd quirk: If I'm really deep in a depressive hole, I can identify that by writing a journal entry. If I start freewriting and the content is getting progressively worse (usually devolving into sentence after sentence telling myself to grow up and kill myself), I can sometimes "trick" my brain into realizing I'm in a depressive hole and the world isn't actually an awful place.
It's hard to explain, but the ability to "see" my brain thinking in a downward loop sometimes helps to trigger my rational brain.
On the flip side, in some rare instances if I journal while depressed, it dramatically increases my misery. Instead of just thinking I'm hopeless, it can work as a mental reinforcement that everything I'm writing is true. Journling while depressed is like playing Russian roulette.
Overall, I don't find journaling that beneficial.
There is medical evidence that it helps in depression. It might not elevate your mood the same time but you can see the pattern and how stupid your thoughts are some time.