If we are filming a panel discussion, live workshop or some other event, we need two cameras to ensure nothing is lost when swapping out batteries, memory cards or in case someone walks in front of one of the cameras.
But for controlled talking-head situations when we can control when to roll and when to cut – one camera is advantageous. The secondary reason it that it is significantly less work during the shoot as well as to later edit.
The primary reason though is that visually, we want the viewer to feel that they are being directly engaged. This means we want the presenter looking directly at the camera.
When we have tried to add dynamism by cutting briefly to a side shot, the end-user feedback we have received, in no uncertain terms, is that they feel we have diluted the authenticity and the content appears disingenuous and distinctly less trustworthy. A single angle has more impact.