In other words, you can create your own Multimedia with HyperStudio.
Multimedia means creating a document or program that uses several distinct media.
Text is a medium. Graphics are a medium. Sound is a medium. The theory is, the more media, the more appealing and interesting your document or program. Of course, too much of a good thing can indeed be too much, but as the author of a HyperStudio stack, you can make sure that your document uses the right balance of media.