What are the advantages of a company working with a union?

What are the advantages of a company working with a union?
First things first, most companies don't up and decide they want to work with a unionized labor force. The workers themselves unionize or join an existing union and the company has to go along with it or lose their entire workforce. It's less a matter of advantage than it is a matter of compulsion.

However, a company can benefit from working with a union. Morale problems and worker suggestions can be handled by the union leadership, which will then bring these concerns to the company and work towards a solution. This improves worker morale without forcing the company to handle every worker complaint directly. Also, knowing their wages and conditions are union-mandated helps workers come to terms with conditions that are less than ideal -- there is a standard for acceptable conditions, and workers may complain less if conditions fall within this standard.