|Build. That. Tension. (Okay, that was overkill, but you get my point.)|
In an essay, most sentences have similar sentence structure. The writer wants each thought to flow smoothly into the next. Changes in sentence length or tone can be jarring for the reader, and are rarely used.
But the same abbreviated sentences that don't work well in essay writing are an important weapon in the fiction writer's aresenal. Compare these two passages:
"The hell hound growled, and Carly froze with fear. She felt the other-worldly beast's breath hot on her neck, until finally her limbs loosened and she was able to run."
"The hell hound growled. Carly froze. She felt the other-worldly beast's breath hot on her neck. Her limbs loosened. She ran."
While both passages say essentially the same thing, the second conveys tension not only in content but in structure.
A similar example outside of writing is the difference between instrumental easy-listening music and instrumental movie scores. While on the surface they may seem similar, within each song easy-listening music tends to flow smoothly without abrupt changes in mood. Contrast that to movie scores that often slow music down, speed it up, switch to minor key, or make a few notes louder or softer to convey changes in mood. The movie JAWS wouldn't have been quite the same without it's famous "Duh-da, Duh-da, Duh-da," score. This is the same thing we can do with sentence structure in fiction writing.
Have you experimented with varying sentence structure to increase tension or change mood in your writing?