Hey, don't knock those doggie bags; the wife and I have been known to get two more good meals apiece from those leftovers. I wouldn't dare go to all-you can eat buffets more than rarely, though; between my inclination to get my money's worth, and my plain lack of self-discipline, things could get ugly.
Then again, there is the approach to buffets that a couple who were co-workers with me practiced and bragged about; go in with shopping bags, eat all you can, and smuggle out all you can in the bags. (If you had known these people, you probably would have wished you didn't).