I remember one of the refrains from a professor of mine at Stark was 'Always fire the caterer after the first few days.' It was from someone I have a tremendous amount of respect for, who was a producer on Seinfeld, among other hit TV shows and movies.
It was said in a joking manner, but only slightly. The lesson was that you need to exert your power on the set, while showing the crew and cast that you care about them. And of course the caterer might suffer, but they are the sacrificial lamb.
This lesson definitely did not escape me when I had to fire the caterer on White Space after a few days. I didn't set out to do this... but the food wasn't that good, and it was a goal of mine that the crew and cast be served the best food possible (for our budget). And the guy serving it was creeping me out. I just found it pretty funny that the first person to fall under the axe was the caterer, after this lesson imparted on me back at USC.