Soundtracks are an imperative part to story telling in films. Like light, shadow, color, and any other visual aspect of film, film music fills the same role of mood prescribing. This can be attributed to the five senses and the fact that film only has access to two of them. Thus it is a necessity that the director utilize every tool at his command.
Take, for example, in The Girl With the Dragon Tattoo (2011, American re-make) directed by David Fincher and compare it to the original from Denmark (2009)’s final climax scenes inside the murders torture chamber. The music chosen in David Fincher’s being Enya’s ‘Orinoco Flow’ is a stark contrast to the tension created by the visuals. This song is in movie (in movie meaning the characters can hear the song, unlike a background songs [any song in the film Gladiator]). This song was purposely chosen by the killer to exacerbate his image as a psychopath, in that he finds a kind of mellowing by torture.
Film music isn’t just a great mix tape (although Quentin Tarantino might disagree with that statement). But it is also a tool to engage the viewer in an experience, evoke emotion, and transition through time periods.