Yeah they really do vary a lot. Something I did not appreciate until getting my first as an adult (as a child, I had no positive feelings towards dogs which I find sad now).

I have heard trainers who suggest meal time is meal time, the food is taken if it is not eaten, it's not a self-serve grazing buffet. I think part of it is about making it clear who is in charge, especially if a dog is not listening during training, but there are other reasons I forget like resource guarding and predictable toileting. But we all decide how much we let them express their personalities :)