Years ago it was common if you filled a car with gas to the top, and then parked it in the sun for the afternoon, you would see the “expanded” gas leaked all over the pavement.
In today’s vehicles, filling a gas tank to the top means you run the risk of damaging your car’s evaporative fuel recovery system (charcoal canister). Some cars are more sensitive than others. Topping off today’s cars isn’t worth it.