The first time i kept a journal was when I first went to Europe. At first it was not much more than bullet points; factual summaries of my day and sights seen. On my second trip, while riding on a train doing the same bulleted list, I suddenly flowed into a more detailed description, taking into account what I was thinking over the previous days and even what was going on while I was writing. I've followed that format with subsequent trips and I'm glad I did. I also started doing the same with my personal flying. After each flight I would write down mistakes, successes, etc. just to have something more than the short descriptions in my pilot logbook.
I never considered doing the same while home. I'm constantly thinking, and I think it would do me well to put all that down on paper and get outside my head. I've reconsidered it now that I have a son, and I realize already that there is so much that has happened in the last year or so that I've already forgotten.