In education, Plato put more importance on math and philosophy (and abstract ideas - Forms) than on art, poetry, and music. He believed that math and ideas were much closer to the truth while the arts were merely imitations of the truth. Especially where morality and justice are concerned, Plato felt that the government should be run by philosopher-kings, those who understood the difference between Truth and images or representations of truth - made most famous by the allegory of the cave (Book VII - I think). Otherwise the government will be led by those who misinterpret Truth or interpret it for their own ideologies or favor the wishes of the people. In this sense, Plato's Republic would be not quite as democratic as it was during the time he wrote The Republic.
That being said, Plato makes it a point to say there's always been a quarrel between philosophy and poetry, or analogously, dialectic and rhetoric. And remember that poetry in Plato's time meant something very different: it was more about seeing live performances of rhetoricians reciting The Odyssey, not sitting quietly reading verse. The reciter is at least once removed from the author and the written text is likewise. The text, unlike the author, cannot answer questions; and the reciter can only speculate about the author's meaning. Here is reason why Plato felt poetry was more removed from the truth: a hierarchy with Forms and Authorship and Presence on the top - Presence (of the author and listener/participant in a dialogue) allows a dialectic: a conversation between author/philosopher and audience. For Plato, poets are just imitators: Xerox machines who cater to the emotions of the audience. Philosophy is objective, the arts are subjective.
Ironically, Plato's dialogues which are primary examples of dialectic, are written with a certain kind of poetry. Maybe a subconscious attempt to compromise the quarrel between philosophy and poetry.