Basically, the author did studies and interviews and found that some couples who fight frequently do still have a healthy marriage.
This goes against some common-sense notions, of course.
The important thing was that each thought the other one heard and understood their point of view. I can't recall if the feeling that progress was made to resolve the dispute mattered as well.
Marriage Satisfaction = Fighting (or Total Conflict) - Unresolved Conflict
Conflict among other things brings you closer together. A couple who "fight" well will stay together.