What is meant by "Do not push" on the back of dump trucks?

Factual Questions
1

Hello Everyone,
I was following a dump truck this morning and in big letters on the back it said DO NOT PUSH. Of course I’ve seen this all my life but have never quite understood what they mean. Do they mean don’t tailgate? Dont push with another vehicle if it’s unable to start? What does it mean?

2

See previous discussion on this topic.

3

Thanks

4

A week or so back I saw a dump truck that had Caution, do not feed the driver! stenciled in a lovely script across its back. What happens if you feed the driver?
NB: I really did see this. I have pictures.