Баба с возу - кобыле легче
I think it means that when a cart gets stuck in mud or something everyone redundant should get off the vehicle so the horse could easily drag it out of the mud. The man can't go off because he is a driver.
but
I think it can mean a veiled thought that the woman can spoil a pleasure so if she's off it will be even better.
Imagine a peasant packs things like sacks with grain on the cart to go to the marketplace or to the landlord to sell it and get some money, part of which he can use first of all to buy some samogonka right away after he sells the load. But the woman will take all the money and destroy the dream. So if she stays home the man is happy but in order not to reveal why he is happy he thinks up the excuse

Научному исследованию вопроса от том, насколько же именно кобыле легче, если баба с возу, посвящена диссертация под названием "Оптимизация динамики работы гужевого транспортного средства путём устранения изначально деструктивной транспортной единицы".