If you fill up your fuel tank when it’s only half empty, here are some good reasons to wait till it’s nearly empty:
1. You will cut down the number of your trips to the gas station. That will save you time and money. It will help save you money for two reasons — you will do fewer impulse purchases at the checkout counter (if you pay there) by paying for the fuel fewer times. You will save the fuel that it takes to stop and start your car or driving to the station, if you made a special trip.
2. You will pollute the atmosphere less. If people idle their vehicles behind you when you’re fueling, you’ll prevent some of their emissions from entering the atmosphere.
The only positive reasons I’ve heard to fill up sooner are that there may be sediment in the bottom of your tank that could get stirred up if the fuel level goes too low. But modern engines have sophisticated fuel filtration systems, so that shouldn’t really be a problem.
And yes, you are smart enough to fill up early enough that your tank won’t go empty.