A story that requires something more than what one form a communication can provide, is a story that can be succesfully told through multimedia. It can be as simple as adding music to a film, pictures to a news story, or video to a blog. Multimedia should be used where the story can be enhanced by it, either adding more emotional depth or information that cannot be conveyed with wrods, pictures, or video alone.
Your basic business article, or scientific report (as reported by newspapers) dont neccesarily lend themselves to multimedia, as straight fact telling doesn’t necceasrily need visuals with it. Just as many pictures dont need words to describe them and many films function quite well without an interactive aspect. But what’s the sports page without pictures, or the website without clickable links, or the video game without narrative? These mediums are enhanced with a bit of “extra” content.
For example this story about art spaces during the economic recession woudn’t be the same without it utilizing multimedia to allow the user to both hear the voice f the gallery owner and see pictures of the art featured in his gallery. http://www.nytimes.com/interactive/2009/06/21/arts/design/20090621-artists-feature.html?ref=multimedia