Writing can be a cathartic process. It enables a person to be able to dislodge from inside themselves the pain they have just traversed. So by writing about the painful processes we seemingly cannot avoid is a way of dealing with this. If we hold all of this pain inside it can cause a person's health to fail. Write it down and get it out - this is the remedy.
Sometimes people write down their feelings and burn these. Some even put them in the freezer. I like to write for history and so when I write it reminds me there have been good and bad days.
I like the Led Zeppelin line that say's, "On every day a little rain must fall". Writing about the rainy days and rainy hours and the rainy minutes is a beautiful thing for yourself.