With singers or musicians, you can hear them whatever the camera is doing and though the visual performance is a factor, it's the voice or instrumentation that is the main decider.
With dancers and other performers, you need to see the whole act to appreciate it.
Unfortunately, it's something else that can be used as an influencing tool. Kate and Gin, Nemesis, Strike, etc are about to perform a move that could have everyone at home wowed and increase the likelihood of the public reaching for their phones for them and ............... oh, dear ............. coincidentally, they cut away to the judges or the audience or Ant and Dec .................... and lo and behold, the move is not seen.