I come across this fairly regularly. People who had enough to eat but say I will finish that off so it does not get wasted. I don't understand that. People do not want the food thrown away but it is not considered a waste to eat more than you need.
My brother does this with his four kids. If one of the kids does not finish what is on the plate then the other kids have to eat so it does not get 'wasted' even if they are saying they do not want it.
I don't like waste either but I am not going to eat more than what I need just so it does not get thrown away. I would rather it get thrown away than just eaten when not necessary.