Transporting New Information With Music
The ideal function of film music is to add something to a scene that isn’t already transported by the pictures. Film scores that solely focus on doubling or commenting the information that are already transported by the images feel quite flat after a while.
However, in the real world, many movies don’t leave much space for adding another dimension to the scenes which will leave you to do nothing more than just writing music that doubles what we see already. So the ideal that is taught by many film scoring text books is realistically not always achievable, not even by the best composers.
The important thing is to actually not miss the scenes where you actually CAN add another dimension, so always be conscious if in the scene you’re currently scoring there might not be something to be told by the music that is not being transported by the images.