I’ve found that how much more fuel can get in the tank after the automatic shutoff varies greatly from car to car. My Mustang is pretty much filled to brim once the pump clicks off for the first time. But my Bronco can typically hold another 2 or 3 gallons after the pump clicks off the first time. When the Bronco was my daily driver I got into a habit of topping off. With the Mustang that’s not really possible. As others have mentioned, topping off the tank can lead to problems with the Evap system. I know it does happen, but I’ve never had problems with it despite years of topping off the tank.