Picture and Sound as Collaborators

Music, dialogue, and sound effects can each do any of the following jobs, and many more:

* suggest a mood, evoke a feeling
* set a pace
* indicate a geographical locale
* indicate a historical period
* clarify the plot
* define a character
* connect otherwise unconnected ideas, characters, places, images, or moments
* heighten realism or diminish it
* heighten ambiguity or diminish it
* draw attention to a detail, or away from it
* indicate changes in time
* smooth otherwise abrupt changes between shots or scenes
* emphasize a transition for dramatic effect
* describe an acoustic space
* startle or soothe

exaggerate action or mediate it.

At any given moment in a film, sound is likely to be doing several of these things at once.
But sound, if it’s any good, also has a life of its own, beyond these utilitarian functions. And its ability to be good and useful to the story, and powerful, beautiful and alive will be determined by the state of the ocean in which it swims, the film (Randy Thom, via FilmSound.org).
Here is a short example of sound used in an organic and powerful way, Nissan 4x4 Naturally Capable ad.