Experts will advise that you should pause regularly during a meal to evaluate whether you're full or not. And I hear in some cultures it's polite to leave a bit of food on the plate; it signals to the cook that he or she has provided in plenty. That's not the culture in my house.
I am what is called greedy. Not indiscriminately. But if something is delicious, I'll eat every last morsel. So at home we portion accordingly. Hence this roast dinner: a chicken each, and two clean plates.
(Favourite bits: the caramelisation on the bird, and the whole roast clove of garlic, infusing the rest of the vegetables and providing a little package of immune-boosting tastiness.)