In a way this is a phony dichotomy. Good art – what in the advertising world is called “production values” – is very important to the effectiveness of most marketing.
BUT I can’t stress enough that art is there to SERVE marketing. Art Gone Wild wins Cleos (Ad Industry awards) and loses business for their clients and accounts for agencies. This is called The Curse of the Cleo.
Encourage designers to knock your eyes out with their artistic conceptions and execution. But then step back and see if it communicates or confuses.