I’m not one of these people who complains about the deadweight loss of Christmas. If you want to get all homo economicus, presents are a valuable signal: finding out how well someone really knows you is hard (expensive), whereas buying a book or even a TV is easy (cheap). Potlucks, on the other hand, bug me to no end.
Cooking has obvious economies of scale: cooking ten times as much of a dish takes perhaps twice as long; and cooking ten times as many dishes has about the same overhead, because so much can be done in parallel (and the relative overhead is even lower, if you consider cleanup time). Having each person prepare a single dish is the most inefficient possible way to go about it. Furthermore, not everyone has the same aptitude for cooking: division of labor, people! Worse yet, each person inevitably brings at least one dish or dessert that’s large enough to feed five or ten people (and oftentimes more than one), so there’s an order of magnitude food than necessary, much of which goes to waste (leftovers aren’t as good as freshly made food, so this is lossy even if the food gets eaten).
P.S. If you’re in Austin, and want some leftover pie (apple, pecan, or pumpkin), cake (chocolate), side dishes (green bean casserole, stuffing, or gravy), meat (turkey or chicken), or meat substitute (seitan or tofu) let me know.