If you are doing a feature on someone who has a specific skill set or does something out of the ordinary, you might want to have video and audio of this person showing off their special abilities. You could also use a slideshow when covering a special event in order to capture everything that is happening.
Audio and video can be used in many different situations, but there are scenarios in which it wouldn't entirely be necessary. In our specific project in covering a conference that we attended, photos and audio would be necessary because we are covering an event that is only held annually. We were able to interview people and the photo slide and audio allows the audience to get a better grasp of what the journalists are trying to do and what the story is that they are trying to tell