When somebody wishes to make a video to show how to do something like use Google AdWords for instance, they require somebody that can talk the viewer through it. If they don't have the time or devices to do it themselves, the rational solution would be to work with a voice over artist to do it for them. Finally in another video classification is tutorial videos or "how to" videos. I've been worked with to do both the audio and video AND simply the audio for these kinds of videos.

Whatever industry you are participated in, every day you deal with competitors, and intentionally or unknowingly, you are working hard to occupy more resources. Admit it - we are in an extremely competitive world.