1: Better gas mileage. When your wheels are aligned properly, it cuts down on rolling resistance, which means that you car doesn't have to work as hard or burn as much fuel in order to move forward. This is good news for everyone: Not only do you spend less money on gas, but you also get the satisfaction of knowing your car is responsible for less pollution.
2: More mileage out of your tires. Even the slightest problem with your alignment can have disastrous effects on your tires. If your tires have too much or too little toe-in (the degree at which they point in toward each other at the front, like a person who stands pigeon-toed), a narrow strip on each tire will wear down very quickly, causing you to have to get new tires sooner. By getting regular wheel alignments, you ensure that your tires wear evenly, making them last as long as possible.
3: Tire warranties still apply. The problem with your tires wearing from poor wheel alignment is that it usually voids your warranty on the tires. Most warranties only apply to the quality of the goods. In other words, if the tires wear out too soon because of something other than poor quality, then the manufacturer is not responsible. Failing to get wheel alignments often enough is considered to be negligence on the part of the car's owner, and usually means that the warranty is voided.
4: Less wear and tear on other parts. Having the wheels out of alignment can be stressful on the rest of the car, too. It means that you continually need to put pressure on the steering system in order to keep the car straight, and when you brake you often feel the car pull even more sharply, indicating that the brakes are needing to work harder on one side than the other.
5: Easier to drive. One of the biggest advantages of having your wheels aligned properly is that your car is easier to drive. No annoying pull to one side or the other.