In hopes of assessing how many one sentence paragraphs I had in my novel, I changed the magnification on my word processor window, which made the text appear much smaller than usual. This allowed me to see most of a page on one screen. As I scrolled through the pages, stopping whenever I saw a one sentence paragraph, I joined what I could with longer paragraphs, and omitted some. This was prompted by a piece of advice in Francine Prose’s Reading Like A Writer, namely not to overuse the one sentence paragraph. As I combed through the text, some unexpected things happened:
1) I realized that sometimes one sentence paragraphs are necessary, the best choice. I want to trust the reader, and not lean too heavily on the structural signal of a one sentence paragraph as alert: “Hey you reader! Look here! This line is so important I set it up on its own! Read carefully!” And yet sometimes a one sentence paragraph just feels right. (It was good to interrogate each occurence, however, to be sure.)
2) The decision about where to break paragraphs has its own intuition, and the writer should take time to quiet down enough and follow it.
3) I was doing a lot of changing and then changing back, doing and undoing. A lot of tinkering, but maybe the act of tinkering confirmed that I’d gotten some bits “right” before questioning, if such a thing as “right” is possible in a thing so subjective as fiction.
4) Another nuance I hadn’t considered, in defense of keeping some one sentence paragraphs in this novel: my protagonist is seven years old. The child’s close lens on her world and the visual smallness of a one sentence paragraph seem connected. I don’t think this is overly precious, in this case.
5) The exercise was a great lesson, and proved the point that Prose includes in her book. On p. 68-9, she quotes Rex Stout’s novel, Plot It Yourself, in which “Nero Wolfe is called upon to determine if three manuscripts that figure into a case involving accusations of plagiarism could have been written by the same person.”:
“A clever man might successfully disguise every element of his style but one–the paragraphing. Diction and syntax may be determined and controlled by rational processes in full consciousness, but paragraphing–the decision whether to take short hops or long ones, and whether to hop in the middle of a thought or action or finish it first–that comes from instinct, from the depths of personality. I will concede the possibility that the verbal similarities, and even the punctuation, could be coincidence, though it is highly improbable; but not the paragraphing. These three stories were paragraphed by the same person.”
So is the paragraph like a fingerprint, individual to each writer? Maybe.
Another thing happened as I worked through the manuscript, not related to paragraphs, but worth noting. As the text looked so much smaller to my writing eye, it performed a visual trick on me. I’ve done this bird’s-eye thing before, but this time I was pulled into some scenes despite (or maybe because of) how hard it was to read the words. The clusters of words formed different shapes in my brain, pulling me in. Like those little sugar Easter eggs that you peer into, I had to look closely and see the world that was hiding there. And thus I did a whole lot of unexpected line editing than I planned to do. Good.
As always, I hope it’s stronger for the toil.
Rebecca Kuder 
Rebecca, I think the idea of paragraphing as a writer’s fingerprint is a valid connection. I think it works basically the same with section and chapter breaks. Also, I, too, spend rewriting time making changes, putting the text back the way it was, and then making the changes again. I’m glad to hear that others do that as well. :)
Lisa, yes, you are not alone, and I’m glad to hear I’m not either! Such an obsessional job. I once saw the Indigo Girls in concert, taking a really long time tuning their guitars (because I guess a lot of their songs use different tunings) and Amy Ray said, “We tune because we care!” I think other singer say that, too. I think revising and refining words is similar.