One problem with using the same sentence structure over and over is that it's boring. It's boring to write, and it's boring to read. Take a look at the example below.
We went to the amusement park. We rode on the rides. We rode all day long. It got dark. We watched the brightly colored lights. We had fun.
Boring.
Another problem with repeating the same sentence structure over and over is that it can make the relationships among ideas and events unclear. More complex sentence structures, besides being more interesting to read, give your writing clarity, or clearness. Using a variety of sentence structures lets you share simple ideas simply and complex ideas with the additional precision they require. Note how this revised example reads much more clearly than the passage at the top of this page.
We went to the amusement park and rode on the rides all day long. After it got dark, we watched the brightly colored lights. What a fun day we had!
Question
How is the revised example different from the original?
The revised example eliminates many repeated words. It combines the short, choppy sentences into longer, smoother ones. It shows time relationships ("After it got dark"), and it communicates more of the writer's enthusiasm.