It's helped me feel better, be in the present, clarify my thoughts, get inspired, vent majorly, and always been there for me. Journaling through the years has been like a good friend. I like it the old fashioned way pen on paper. Somehow, writing on the computer is not the same. I just pick up a pen and dash off on how I'm feeling or what I'm thinking without regard to grammar or spelling. In the end of it there is always a slight lift in my mood and it helps me observe what is really going on in my life. In a way, apps like Instagram and Facebook, are carefully curated journals of our lives, but nothing beats the fierce pouring out of emotions and ideas on to a page.
People write all kinds of journals, gratitude journals, journals of affirmations and quotes, art journals, you can even find prompts on Pinterest to begin writing. The kind I like have not just the words but ephemera from the day, newspaper clippings, petals of flowers, theater tickets, photos, drawings, and so on. Two examples of these are the famous photographer Peter Beard's Journals, and those of Dan Eldon.
Here is a picture from Peter Beard's journal.