There were two sisters in the film as well as in my story. They fell out with each other in a fairly spectacular fashion and it really livened the pace of the film. I felt that my sisters needed to do the same, instead of ambling through the story in a pedestrian way. I'd written them into a rut.
A good row is helpful for allowing home truths and past grievances to emerge. These can round out the plot and heighten the tension. Stories need progression and any sort of conflict leads to an advancement of some kind. The pace speeds up too. Dialogue becomes quickfire. Don't forget to let the characters interrupt each other, as this is always the case in reality. There is less listening and more revelation.
So enjoy a good row!