From a user perspective it is hard to know whether the webcam LED is software controlled. If it is software controlled, e.g. by the webcam driver, it is prone to manipulation and could remain off while the webcam is recording.

Of course, there are many cameras that do not even have an activity indiator (LED), e.g. stand-alone cameras, or simply your phone front and back camera. I find it a good habit to cover all cameras, regardless of wether they have an indicator.