I was getting gas the other day and noticed the person on the other side of the pump doing something that made me wonder how many people do the same thing. Do you keep pumping gas after the first click? I know,  I know more gas in the tank means you can go further before needing to gas up again right? Well this may be true but topping off the tank may also be harming some components that could eventually cause the check engine light to come on and also harm gas mileage. The evaporative emmission system that channels your fuel vapors back through the engine to be burned as fuel is not designed to handle fuel in the liquid form. Topping off the tank to the point where the gas almost runs out of the filler tube allows the liquid gas to enter those components causing damage. The gas pump is designed to click and cut off when the gas backs up the tube is considered full. My advice is to stop on the first click and save some possible expensive repairs. Along these same lines never leave the car running while fueling, that can also set off the check engine light.