We argue sometimes. Talk has a disadvantages. You shoudl understand what you want to say, you have to plan your time with your partner, and always there is a probability to itnerrupt each other and continue argue.
I do not remember when we started to use our letters method. It is an old and useful practise for us.
We write letters to each other if we want to express disagreement, dissatisfaction, if something went wrong and make our life uncomfotable. We use usual notebook for this purposes. Everybody writes what they want, what is important for him/her. Often we read it and duscuss. It seems to me dialog is more constructive after that.