I had the pleasure of visiting my friend Floyd in Chicago recently. He runs Complete Crewing, a production company in Chicago. Basically, they take care of all the labor for convention centers like McCormick Place. What I found particularly interesting was that they've carved out a niche, by basically knowing more about one particular area than anyone else.
The labor laws in Chicago appear so byzantine, that some companies bypass Chicago as a site for shows, and others need a resource to navigate them. That's where Floyd comes in. They've got complete guides to venues (in many cases,more thorough than those venues) and due to the frequency of their work, relationships with all of the unions. Fascinating to see in action - and a great old brick building for a workplace.