Yes. You should keep one. I wish I had. After my father passed away I found his in his sea chests. The entire pacfic war. He was a battleship sailor.
It was. Brought tears. I spent 25 years in the navy. Never kept one. Wish I had. Do it.
I find it to be extremely helpful. However, so I don't have to worry about other eyes reading my thoughts, I tend to keep an online journal. Less likely to fall into the wrong hands, so to speak. It's a great way to get my thoughts out of my head, so they don't stay and fester. The purpose for mine is to vent. Plus, over time, it's neat to look back and see where you were. Like, what you were doing a year ago today.