The sound drives the story by, as Abumrad says (videos below), helping you paint an image in your head. He also seems to point to a connection between the storyteller and the audience. While the storyteller can give you details, every listener will imagine the story in their mind slightly different. After all, I’m sure no one pictured Moon Graffiti in their heads the same way. Sound drives the story by setting the scene and then helping guide you through the events as they unfold. The sound effects and music impact the mood by helping create a setting and, for example, in Moon Graffiti, certain sounds set you on edge, like when they had their rocky landing on the moon. Other sounds build tension, such as when the air supply was starting to run out. It can also speed up the story, since instead of saying or writing something, for example when someone takes a picture in the story, the author can simply have the sound of a camera going off.
However, despite all this, I think purely audio media is my least favorite form of media. I think since there is nothing to look at I end up looking at something else and getting distracted and missing big chunks of the story, especially if it’s not something I’m fully invested in.