With web sites, sounds can let readers know that they clicked on a link, or that they came to the right page. Sound can help describe your content, or intensify the meaning of your Web page. Think about how much impact a site on poetry could be if you heard the author actually reciting their poetry. Sometimes poetry takes on a whole new meaning once it's spoken. Adding sound clips to a site on musicians helps readers understand who the musicians are and what type of music they play.
Sounds can add drama and experience to web sites.
Adding powerful sounds to powerful graphics can intensify a readers experience and help readers grasp what you're trying to say.