Plato, the notorious greek philosopher, had a very specific way of viewing the arts and their meaning to society at the time. To Plato, art was a way of imitation because the artist copied what was infront of him it was a sort of plagerism of reality. He considered the artist's point of view limited and far from the truth, which he was obsessed in attaining.
Even though he thought that art was far from the truth, since it was only a copy of reality, he recognized art's power over human being's emotions. Both plastic arts and music were efficient tools to cause emotional reactions from the viewers, and therefore an effective way of teaching. He thought the influence art had on human emotions could be dangerous at times, that's why it should be used as a didactic instrument.
In conclusion, art was only valuable to Plato if it produced emotional outcome in the subjects exposed to it, and this influence should be used to educate the masses, not to try to represent reality since it could never be completly accurate.