There is an advantage to using the cooking system to process food. On it's face, there is a built in reward mechanic but it is only on the material side. One gets three meat stews for the price of one meat and one veggie, which means that for the cost of two food resources one gets three food resources and those three foods count as both meat and veggies. One gets three fishcakes for the cost of two grain and one fish, and those three foods count as both grain and fish. These prepared foods satisfy the "Likes" requirement for both of their base food types so the slave/peon/follower achieves the "favorite food" loyalty bonus when consumed normally or improves "mood" when on a date unless their "Hates" food is the other component which results in the pros and cons cancelling each other out. Essentially, the benefit from cooking these foods is to stretch food supplies if one is running a particular deficit, which is resource management.