Fingerprint also works with a mask on. Think cold places and big polluted cities. Almost everyone wears a mask in Shanghai if they can.
Face unlock works with gloves on, think winter :)
Oh, and it works when your hands a slightly wet, or when they are very dry.
Some of the higher quality face unlock uses a dot matrix of IR projected onto the face. Should be visible in dark. Might be hard in areas that are bright in the IR spectrum though.