The suggestion to keep a daily or weekly journal is not new. A quick Google search of the term registers over 5.3 million hits. You can be old-fashioned and write in a notebook. You can buy special software to help you keep your journal. But, maybe you have wondered, why journal? Writing down my random thoughts, or what I did today serves what purpose? I have better ways to spend my time.
From someone who starts lots of journals but rarely keeps them going for more than a few months, I understand the questions. For the record, I am not keeping a journal of any kind now. Frankly, the attention I am paying to this blog fills the need for me. However, there are very legitimate reasons for you to consider the experience. Wherever you are on the retirement timeline, journaling may be a positive experience for you.
One of the books I have listed under the Books You May Find Useful link is Julia Cameron's The Artist's Way. She is a big believer in journaling, though she calls it writing your "morning pages." This is an exercise to force you to write. You must complete three pages a day. If you can't think what to write about, write one sentence over and over until you fill three pages. Her contention is the act of writing will help you uncover your creative side and allow you to express anger or gratitude as appropriate to people or things.
A book I re-read at least once a year is Jordan Ayan's Aha, 10 Ways to Free Your Creative Spirit. He likes to call this process Power Journaling. His ideas for keeping any kind of written record includes some I hadn't thought of before. He suggests a focus journal in which you write everything you can think of on a specific theme or topic. The idea is you notice gaps in your knowledge that you can then fill. He describes a Dream Journal, a Letter Journal, a Techno Journal. I won't detail what these are about. Get the book and check it out.
I have kept a Gratitude Journal off and on for years. Very simply, once a day or every few days, write down three things you are thankful for: a pretty sunset, the lawn service didn't break the sprinkler head, you spouse made your favorite dinner, air conditioning, you figured out how to stop the DVD machine from blinking 12:00...anything. This helps you focus on the good things in your life and reminds you that things could probably be a lot worse.
Along the same lines, I have heard of a Beauty Journal. Again, making note of things that please you visually helps train you to notice the world around you and remain positive. A Creative Writing or Poetry Journal may make sense to you. How is this Retirement Thing going so far? That could be a fascinating journal forv you to review over the years. Here's a link to a site that lists various journal options. They are selling supplies, too, so just look at the list to get an idea.
Bottom line. The reasons for journaling and the type of journal you keep are personal decisions. But, I can vouch for the value of putting your thoughts on paper or in a computer. The discipline of doing it regularly is helpful in all areas of your life. You are likely to discover something you didn't know about yourself in the process. You may open up an entirely new area to explore you hadn't thought about before as you develop your own retirement lifestyle.
Journaling is just a way to force you to think and express yourself, and that sounds like a good thing.