Music in film adds a symbolic appeal to the film that cannot be captured in any other way. For a quick example, in “City Lights” a silent film by Charlie Chaplin, when music was added, they used the same musical score for every time the blind girl came onto the screen, it was a way to represent her as a character.
A certain song in a scene of a film, can affect the emotion of the viewer. If in the scene someone is burying a loved one, you wouldn’t play a fast paced song with the intention of getting the audience excited. You would instead play a slow somber song with the intention of capturing the emotion of the character and transferring it to the audience.
It doesn’t even have to be an entire song, just a few simple notes can increase the tension of a film. Like in Jaws, the same two notes being played on repeat with an increasing rate. Those notes increase the tension in your seat that you want to yell at the screen to warn the character that is about to meet their end.
Accomplishing this type of emotional appeal can be very challenging and not all directors are able to achieve this. Action film songs will sometime just have a random rock song in the fight scene just to provide a great fast paced song to go along with the actions happening on the scene. However the song will provide no emotional appeal to it
Music in film can do a lot to improve the quality of the film. From effecting the emotion of the audience to increasing the tension of a scene. Film would not have the effect it has without the music helping.