Around our house, we definitely cook with the expectation of having leftovers. While we do plan ahead some, a lot of our meals involve looking in the fridge and trying to figure out something to make with whatever raw ingredients happen to be in there, and hopefully scaling whatever spices/sauces/etc to match. It's only two of us, and we'll often cook 8-10 servings of something to have lunches for the next couple of days.