It's not specified, but I assume that you're asking about the visual arts: paintings, drawings, sculptures, etc. I had a week of art history classes this summer taught by the director of the local university's museum, so I know a little bit about this topic.

Most art is made "for art's sake" - that is, to be viewed and judged and appreciated. In this case, while trivial, art is meant for delight. Humans decorated clay pots, not to make them more practical, but to be pleasing to the eye and to have something to do. A form of entertainment then, much as we visit art museums for entertainment today. Other than entertainment at the time however, such creations now only serve as insight to the cultures of the past, which is valuable in and of itself depending on who you're talking to.

More current functions of art include communication, commentary, and persuasion. With communication I refer to areas such as graphic design, where people communicate ideas, beliefs, and other messages through their art. Commentary ranges from impressionist art to political comics as statements on whatever the artist wants to make a statement about. Persuasion can be done through either of those two or another way, but the basic idea of persuasive art is simply to persuade the viewer to agree with whatever the artist is proposing. It could be persuading you to believe that one thing is better than another, or that we need to rally against a perceived enemy.

So I suppose that art, today, isn't directly beneficial to society aside from expression, and could potentially cause harm if some persuasive art succeeds in persuading a group to do something bad. In the end, art is only as valuable and beneficial as a person decides to make it.

Art museums, on the other hand, are economically beneficial, but I won't get into that because this is already far too long and it was only briefly discussed in class. I hope this helped answer your questions!