When a gas station has its underground tanks filled, the particles at the bottom of the tank are stirred up. These particles can become mixed in with the gas that you are putting into your car, which can lead to efficiency problems. The particles can clog your fuel filter, causing your car to stall and start with some difficulty.
If the gas station that you have decided to stop at has the lowest gas price in your area, you may want to think about taking the time to come back at a later time rather than stopping at the next gas station that is offering a higher price for gas.