Although you can generalize to create one, art plays many roles in society and each is too deeply meaningful to fairly be lumped with any other.
One that I've been thinking about today is art's role as a tool that allows us to communicate difficult or intense thoughts and emotions. Even in this aspect art has multiple facets of utility.
I read an article today (URL is below) that illustrates, for me, the beauty in art servicing as a way for people to speak by proxy. To have their feelings and thoughts elucidated by someone who has the words to do so. It's as old as art itself-- so many song lyrics have been printed out and handed to someone with the comment "This is how I feel. This song says it all."