Well, I think you might need to be more specific in your question. I mean, the obvious answer is: whenever the stock lens won't get you a wide-enough field of view.
Other answers would include, say, when you're working with a steadicam or glidecam type of device, or doing a lot of handheld run 'n' gun type stuff... the wider field of view can even out some of the shakes.
Or when making rap-style music videos.
On other cameras, like the VX2000 etc., you almost always had to have a wide-angle adapter in your kit bag. With the DVX, the stock lens is as wide as a VX2000 WITH the adapter, so it seems like most people may not need a wide-angle adapter.
