i've worked at a few startups with catered lunches. where i'm at now, we purposely only cater lunch and not dinner so that people don't feel obligated to stay later. we always have the kitchen stocked so there's food if they do, plus we order extra at lunch so there are leftovers. no one is required to stay and eat, but it helps everyone bond at lunch over non-work related things.

plus, some people go out on their lunch, and come back and eat the food at their desk. win-win. free food, no obligation to work.