I was the one who brought up writing… I saw it on Oprah I think. The point of it is communication. If you cannot talk directly, then write everything down, it’s better than keeping all feelings inside. But don’t blame the other spouse, instead just write whatever you’re feeling at the moment… hurt, angry, pain, etc. Then you sit down and discuss the problems causing the emotions.
The risk of it is if the husband has a tendency to bring up past issues, then he could save that letter and throw it in her face in the future.