Sentence structure variety makes content more readable and improves its overall quality, states the Purdue University Online Writing Lab. Unvaried sentence structure leads to a sense of monotony and repetition in writing. Varied sentence structure reduces repetition and lends a sense of life and emphasis to writing. Sentence variation also can change the emphasis in a particular sentence.
Using too many sentences of the same length and structure can make writing bland, while sentences of different lengths enliven paragraphs and allow for effective emphasis, Purdue's OWL suggests. Long sentences are useful for incorporating a great deal of information. Short sentences can drive crucial points home.
There are more aspects to sentence structure variety than merely length, however. If every sentence begins with the same word or phrase, especially common words such as "the," "I" or "there," the writing becomes repetitious even when there is a mix of long and short sentences. Changing the opening words or phrases of sentences helps to refresh writing and reduce the burden of repetition on the reader. Modifying sentence beginnings sometimes alters the emphasis within the sentence. Altering the emphasis of one sentence can encourage sentence variety in surrounding sentences, meaning that one change leads to an overall increase in sentence variety within the prose.