Most of the times we photograph someone, it’s not possible (or desirable) to include the whole body onto the photograph. In these situations we should be careful how to compose the photograph in order to avoid the feeling that the subject is missing a limb.
To do that, we should avoid to “cut” the person we’re photographing by the joints. What I mean is that if, at the border of the frame, we place the knees, elbows, pulses, neck, etc, the image becomes quite unpleasant to look at. It’s weird, but there’s nothing like trying this out and make this mistake to verify this. What we shoul do is to make that “cut” somewhere in the middle. If we want a simple portrait of the face we should include the shoulders and a bit of the chest; for a more open angle avoid cutting by the elbows and do it by arm or forearm; and the same for the legs.
