With Marty present, Bungie's audio team has always been very meticulous about the whole audio experience. It's a complete package. If they do their job right, the player shouldn't need to mess with the settings. With Marty gone, who knows?
Even if they do it right, I want the option to have no music. None. It annoyed the hell outa me in the alpha when the music would just keep getting louder and louder, drowning out the sounds of combat. I care more about combat than I do orchestras. Let me turn it off.