Here's why:
* Descriptions can be short or long: A simple description of a cat might be one sentence: "The cat was fluffy and grey." A detailed description of a historical event could be several paragraphs long.
* Purpose matters: A description for a product listing needs to be concise and informative. A creative writing description can be more elaborate and evocative.
In general, a good description should be clear, concise, and relevant to its purpose. Whether it's one sentence or several paragraphs, it should communicate the important information effectively.