None of them is required for this, it just steals valuable time from the actual content.
For example when trying to find physical hardware reviews (basically the only reason I can think of where a video can be more preferable to something written). And yet it is incredible how many reviewers think you'll be happy to stare at their faces for the majority of the "review"; practically all this runtime is them advertising themselves.
What else did you want on a video site? You just think they should not include their faces in the videos?