Content development is a horses for courses type affair. If you have a web site then one long article may be the best to deliver the information you have. For blogs, smaller articles are often the best way to go.
The most important components to content development are quality and frequency. The more often you publish pages, the more often you will be visited by the search engines. Just as importantly, the more often you publish the more often your visitors will return.
For a website that contains many pages, a single long article may be the only way to get a message across. However, if possible, try to break it into sub pages. For example, a page on how to use a product could be broken into three or four (or more) pages; an introduction; the basics; advanced use; and maintenance is one example. If the information on the pages is a little repetitive, don’t worry. Work on the principle of someone arriving on that page having not read any of the previous pages. Just don’t copy and paste. Reword each page to keep it unique.
Blogs on the other hand can have longer articles broken into a series. You can focus on the same topics as the previous example, and again, there is no harm in repetition so long as the content is unique.
Whether it is a web site or a blog, release each new page at a regular frequency. If you can provide content on a daily basis then publish each page daily.
There is no ‘golden’ rule to using long or short articles. However, the more pages you have the more opportunities you will have to rank in the search engines.