Imagine you've left and you're up in the arctic on a dog sled.
Your dog team is pulling straight and true. You can cover a lot of ground fast. Now imagine what would happen if one or two of the dogs wanted to go their own way and were pulling off to the side.
That would slow you down. You would have to work harder to keep the sled going where you want it. The dogs are all working as hard as before, but you're covering less ground for the same effort.
You're wasting kibble.
The same is true of your vehicle when the wheels are out of alignment. That wheel that's pulling to the side is dragging down the rest of the car; so you push a little harder on the gas pedal to keep up your speed. You're wasting gas.
So have your wheel alignment checked at least once a year. Get it checked right away if you feel the car pulling to one side.
Sometimes we bump a curb or hit a pothole and knock our wheels out of alignment. An accident can take the wheels out of alignment as well.
So make sure you're tracking straight. You'll save gas and your tires'll last longer. Now, mush!