Most importantly, writers do not allow characters to ramble unless it is a device to communicate nervousness or another trait. Readers and audiences seldom notice well-edited dialogue. Good dialogue fits seamlessly within the story. If a sentence does not fit this law it should be killed. In dialogue, every word is important.
Dialogue breaks the narrative of a story or the visuals of a film.
Readers and audiences pay closer attention to dialogue because it is special. A ten minute conversation condenses into three paragraphs. We talked about our husbands, the kids, and work. Neither of us said anything. Then, she shattered everything.