I write about my health because --
it helps me focus on it. Writing about anything is a good way to think things through. Whenever I had to memorize anything in high school I wrote it over and over and over. It is also a good accountability tool. It makes it more real to see it in black and white on the screen.
I also write about health as a way to help others. Some weight loss bloggers have so many issues and I have found so many who are having a tougher time than I am with this. It keeps my challenges in perspective. Writing is also a way to help others. I know I have read the blogs of others and have been really helped or convicted.
Having things in common with others creates a bond. We get interested in each other and write comments for encouragement and make suggestions. Some are better with words than others but I figure it's all good. Even when we feel insulted it can cause a reaction for better efforts. It can also cause us to choose our words more carefully. We can be reminded of our goals when we are tempted to "stray" because we will have to write about it as well.
It just helps.