[BobS]

In Topic 3:1-3, Rule of Thirds is explained like this:

Rule of Thirds: the frame of a camera is divided into thirds, both horizontally and vertically, using imaginary lines. The best location to place characters in the frame are where these lines come together at one of the four intersection points. The following images show good and bad framing choices based on the Rule of Thirds: (The images are on the topic page)

So even when shooting a documentary, having good composition like this is important for videotaping people or scenery.