I think it is portrayed this way in movies and shows as an auditory que to what is happening inside the mind – clearing the way for calmness. In group meditations it can do the same thing by keeping the collective in sync. Focusing on one thing like a mantra or counting breaths helps to clear out other thoughts and gives you something grounded to come back to when your mind wanders.
Maybe it’s meant as a mantra, kind of tool. Lots of people use a mantra, or short phrase, to focus their breath during meditation. I imagine that it is a similar practice to focus the breath and maintain it throughout meditation!