In the service of clearing ones plate. It can upset the rhythm of the appetite and hunger mechanisms that are part of your body's self regulation.
Eating what you want and need should be the same thing. This is one of the reasons why it can cease to be. Supporting children's respect for their understanding of their own needs is the beginning of practising normal/intuitive/balanced eating.
Far from not clearing your plate being necessarily 'wasteful'. You often find your ability to match your needs to what you put on your plate gets better over time. It's also possible to save things for later i.e. Some like to spread what they eat over a longer period. I found this when I stopped my prescription and cleared up the eating disorder that it had largely created;
Pushing food is not always about getting children to eat more — it’s also about the quest to get them to eat healthy.This is what happened to me in a nutshell. It's about manipulating your appetite-the make up of what you eat-and that can also put you out of touch with your needs, keeping your hunger signals open driving you to get what it requires.
Real waste is actually mechanically eating what you neither want nor need, on the say so of others. That turns your body into a waste disposal unit. And makes someone else's fee fees more important than listening to your body.
That could be a metaphor for how to live in general...... and in more specific ways.
Ironically, or not, it's the association fat people have with being policed from the outside, i.e. not knowing (or being allowed to know) your own mind, that has helped to degrade the general reputation of fat people.