An interesting theory: a face-to-face discussion between intimates tends to move towards either agreement or breakdown. It does not accommodate agreement-to-disagree very well. A recent post at Simple Marriage Project attributes this to "mirroring", the unconscious practice of using the same nonverbal communications as the person you're speaking with.
Face to face communications (in contrast with electronically mediated ones) are becoming something of an interest of mine. Earlier I cited research indicating that only 7% of our meaning is in words, and the remainder in tone and gestures. Simple Marriage gives different numbers, but the idea is the same.
When everything is going well, a face-to-face conversation can increase intimacy. When there's a problem to resolve, however, the pressure to agree may lead to abandoning the attempt before everything can be aired out. And sometimes people just need to think about each others' ideas for a while before talking again. Simple Marriage suggests walking side by side to have a talk like that. Failing that, sit side by side and give each other permission to look at something else. A fire, for example.