This is especially true for Web sites and sales letters. You usually only have a few seconds to capture the attention of your customers in your writing. Keep your paragraphs short. Sales copy should rarely use paragraphs longer than three sentences. One and two sentence paragraphs work great.
Most readers are in a big hurry.
Long paragraphs look intimidating and hard to read. It also looks nicer on the page. Recently an editor of a major national magazine told me he favors articles with two and three sentence paragraphs. The look of the article is almost as important as what it is about.