There were some good comments on the previous post that I wanted to address. First, it is possible that a person could cook more or less based on initial hunger, and then a clean plate would be a natural outcome. I would say that, given the statistics on adult overweight/obesity, that this is a skill that is in short supply.
Also, I was thinking more about restaurants when I wrote the post. That is, a restaurant gives a standard (often oversized) portion to each customer. I would say that unless a person is very hungry, finishing off a restaurant portion could be a sign of disinhibited eating.