Sound plays an important role in telling a story. The wrong ambiance can completely destroy the coherence of a scene. For example, a midnight scene on a highway would make absolutely no sense with rain forest ambiance playing in the background. In my digital media class, we looked at this extreme example of sound completely changing a piece of media. The use of a laughing track and Seinfeld slap bass completely transforms The Shining into a family friendly sitcom.
Music sets the mood for a scene, often without even being noticed.
Listen to the final boss theme for Sonic Rush. Notice how fast it is and how that really makes the entire stage feel super chaotic and frenzied. It takes some of the the focus off of the giant robot and puts it onto all of the lasers and shock-waves constantly flooding the screen.
Now contrast that with the final boss theme for Sonic Rush Adventure, the sequel to Sonic Rush. Notice how much slower it is and how much less emphasized the lead melodies are. Also notice how the bass is lower pitched and more prominent. The stage doesn’t feel as chaotic, but it makes the giant robot feel a lot more imposing. The focus here is directed away from the missiles, turrets, and and lasers and toward the epic giant robot unleashing them.
At times, the music is barely even audible through all of the crashes and explosions going on, but it would still make an entire world of difference if you switched the themes around.