A paunch is more for looks than anything. Just a bit of flesh and feathers.
A breed standard will call for one, two, or zero lobes in a paunch in a goose breeds.
Many heavier breeds will have them while some lighter breeds will not.
Much attention is paid to it because it effects the symmetry of the bird greatly. If a Toulouse, for example, has no paunch, it will be disqualified.
However many lobes a goose has does not matter to the goose itself, though. It’s more of a trait people breed for, like the fluffy feathers of a Cochin.