For some games and some streamers it works.
For others of both it is unnecessary.
Two streamers I watch and enjoy are Markiplier and NerdCubed.
The former relies exclusively on utilising the facecam with every game and incorporates it into his, using an old comedy term, his 'bit'.
He plays up to the camera, engages it and as such it is as much a focus of his routine as the game.
Nerdcubed never uses it, all the humour and work with the game is verbal or through comedically timed editing and in game situations.
Both are making utility of their personality and how they play the game to make it interesting and entertaining to watch, but one uses the cam, one does not.
As such, I'm pretty 'meh' on the inclusion of facecams in such games.
They can add to the video, but with the wrong game or used by the wrong streamer, they can be a detraction from the entertainment.