Let us first try to put our facts together.
In the Book 10 of his Republic, Plato famously attacked arts, on several grounds.
One ground would be metaphysical and epistemological; he believed the knowledge of True Forms to be the one superior form of knowledge, that philosophers should preoccupy themselves with, as opposed to the knowledge of things existing in the world and accessible to us via our senses; which are, he argues, merely imperfect copies of the ideal forms (this is the point of the Cave Allegory). Now, art, as a reproduction of things we perceive with our senses, is a copy of a copy, and thus doubly imperfect. (A painting of a dog is an imperfect imitation of a real dog, which in turn is an imperfect imitation of the idea of dog-ness).
The other ground is more socio-political: art appeals to the emotion, therefore has no place in a society governed by reason; as it can distract from the pursuit of logic/rationality and thus lead as astray from virtue.
Aristotle, who had been Plato's disciple, shared his view that a good society should be governed philosophically and by philosophers, as well as the idea that we should preoccupy ourselves with how to live in a manner conducive to philosophy within society. However, we could read a lot of his Poetics as a response to Plato's desire to banish art from his ideal city.
He dedicates a lot of the Poetics to studying the classical Greek tragedies (you can take Aeschylus' works as a great example, that Aristotle does focus on). In relation to these, he argues that tragedy creates catharsis, a purification or purgation of emotions, or an "intellectual clarification" thereof.
You could argue that while Plato believed emotions had no place in a reason-governed Polis, and therefore art, that appeals to the emotions, is unnecessary, Aristotle saw art (and particularly theatrical art) as a way in which a reason-led society could deal with emotions, collectively, in order to prevent them from interfering with reason. Here is what he writes:
"Tragedy, then, is an imitation of an action that is serious and complete, and which has some greatness about it. It imitates in words with pleasant accompaniments, each type belonging separately to the different parts of the work. It imitates people performing actions and does not rely on narration. It achieves, through pity and fear, the catharsis of these sorts of feelings. (Poet. 1449b21–29)"
You can see the influence of Platonic language and thinking here: art is, indeed, an imitation, but, unlike what Plato believed, it is an imitation that does serve an important social function.