Writing letters can, in fact, help a couple's marriage. This is because it is easier to gather one's thoughts and present them logically through writing.
A letter that is clear, concise, and addresses all sides of an argument benefits a struggling couple the most. A successful couple refrains from interacting in a destructive manner, usually in the form of arguments or passive-aggressive behavior. Instead, the couple channels their thoughts, emotions, anger and frustration in a healthy way, and puts these concepts on paper. In this manner, each person addresses their partner's concerns and presents their own at the same time.