Short sentences are a powerful tool in writing, but their power should not be abused. Long sentences can be used in the midst of medium long sentences, just as I am doing now. A comma can separate a sentence into two parts. Short sentences are impact sentences and should be used as such. A paragraph describing motion, action and the like generally uses a lot of long, flowing sentences which make you speed up whilst reading them. Then a short sentence. Or two. It makes you stop. But then there shouldn't be fifty million of them all in a row making your eyes bleed. The sentences should then keep on going and flowing until the author gets bored of that or it doesn't read well.
Short sentences, when used in their place, create fear, danger and suspense. A short sentence forces you to an abrupt halt, especially after a lengthy paragraph of long sentences. The section in which Kingshaw is being attacked by a crow in I'm the King of the Castle is an excellent example of short and long sentences used in unity to create danger, suspense and action.
A stately room. Hushed. Dark timber. Heavy doors. The sharp smell of polish.
Rising, he stumbled to a window. Stared out.
A great city. Tall buildings of glass. A smudge of brown air. A wide river spanned by stone bridges.
From Quid and Harmony by Allan Smith. Page two of the prologue, to be exact.
The comma in the second line cuts the medium long sentence into two short ones, "Rising" and "he stumbled to a window." The rest of the section seems more of a list than a description. It is hard to read and even harder to create a mental image of the city from the section.
About two more pages of continuous short sentences, of rarely more than seven words, left me without any understanding of the characters, setting or even what the hell was happening. I tried to force myself to read past the fourth page in the book, I tried to force myself to understand what was happening, but the sheer number of short sentences rendered me helpless.