Still, practically, there is some consideration that goes into breaking up paragraphs. I learned from English/writing classes that each paragraph should contain a unit of ideas or thoughts, and a series of these paragraphs would string these units of ideas into one coherent concept or argument, or some such.
That is all good, especially for articles and nonfiction. In fiction, though, this guideline could becomes murky. What constitute a unit of ideas and thoughts?
There are some general guidelines for fiction writing that would hold true under most circumstances. For example, for dialogue, each speaker should get a new paragraph:
"Jane is mean to me," Carl said.
"I'm not." Jane hit Carl on the shoulder and ran.
"See what I mean?"
Also, sometimes you want to pick out a line or two to form a new paragraph for emphasis. It's kind of like a sentence fragment. You don't want to overuse it for emphasis and pace, but it is effective once in a while to set a specific idea/thought apart in its own paragraph. Let it stand out.
However, upon reading my WIP, I realize I tend to write short paragraphs. I tend to move from one idea to another rather quickly, and it seems logical to have them in separate paragraphs. Granted, I don't write 3-page paragraphs describing a lamp! But still, the short paragraphs, I fear, could make my prose read too choppy, too quick, too brief.
Recently I read Ian McEwan's fantastic novel, Atonement, and I noticed how long his paragraphs tended to be. In fact, it seems to be the favored style of literary writers -- Charles Frazier did the same thing in Cold Mountain. For example, in Part 2 of Atonement, McEwan would go on for pages describing the horror of war, and within a single paragraph he would narrate six or seven different ideas, events and actions, that I would have presented in multiple related paragraphs. The effect of McEwan's long paragraphs, however, was one of lushness and languidness that captivated me, with a sense of not urgency or fast-paced actions, but of epic involvement, as if the scenes were one long single-take tracking shot (as done in the movie version, where Joe Wright created a mesmerizing 5-minute long tracking shot of the Dunkirk beach). When I read the paragraphs, that was exactly the feeling I got, as if I was watching that Dunkirk scene in the movie. No fast cuts, no sudden jerks of movements, but a long, smooth but complicated scene (Robert Altman did that a lot in his movies, too -- watch Gosford Park).
That makes me realize, paragraphs are not only used to contain logical units of ideas, but they, combined with sentence structures and lengths, could be used to create atmosphere and movements, as well as altering the pace tremendously. Reading McEwan's novels gives you a different sense of time and place than, say, reading a James Patterson's novel (Patterson favors short, blunt paragraphs for a page-turning experience).
Personally, I've begun to experiment with my paragraphs. I've started to combine or separate them in my WIP to see what kind of effects they would create, and the results are astounding.
As with anything in the writer's toolbox, I think it's important for us to understand the power of structures, including paragraph lengths, to create the kind of feeling and atmosphere we want.