If your vehicles wheels are tracking straight and your tires are wearing evenly then you likely don't need a wheel alignment.
However you should have your wheel alignment at least checked once per year to make sure the wheels are aligned correctly.
Since tires wear out and need replaced every 10 years or 60,000 to 70,000 miles or whichever comes first the the wheel alignment should be done when getting the tires changed or whenever you have front end work done on the vehicle.