Supposing you were unmarried and no children but had moved in together.
Both worked full-time but one earned 20k and one earned 30k for instance?
If it were me I'd want the rent and bills etc. To be paid pro rata according to salary, so the higher earner paid more.
But do you think that all money should be pooled together, and that both should have the same disposable income and savings, even though one earns more?