What is a tire balance
Best Answer:   Start by taking it back where you had the tires replaced, and see if there is some problem with the tires themselves.
Balancing a tire means you look for a heavy spot, and add a weight to the light side so it rotates smoothly.
it probably was smooth because your tire pressure in your old tires were low.
rubbing? did they put the right size?
you should do both.
at high speeds if your steering wheel shakes- get a balance
if at anytime your steering wheel is off center(looks like your turning when going straight) or when your driving and let go of the wheel the car pulls to a direction then a - alignment is needed.
An out-of-balance tire and wheel assembly:
• Degrades ride quality and driver comfort.
• Shortens the life of tires, bearings, shock absorber, and other suspension components.
Vibration is the most noticeable effect of imbalance.
• It is dependent on vehicle speed and may
be felt in the steering wheel, seats or floor board.
• It often first becomes apparent between 40 and 45 mph and changes in magnitude with greater speeds.
Why Four Wheel Alignment?
Reduced Tire Wear
Improper alignment is a major cause of premature tire wear. Over the years, a properly aligned vehicle can add thousands of miles to tire life.
Better Gas Mileage
Gas mileage increases as rolling resistance decreases. Total alignment sets all four wheel parallel which, along with proper inflation, minimizes rolling resistance.
Does your car pull to one side? Does the steering wheel vibrate? Do you constantly have to move the steering wheel to keep your car traveling straight ahead? Many handling problems can be corrected by total alignment. With all the system components aligned properly, road shock is more efficiently absorbed for a smoother ride.
A suspension system inspection is part of our alignment procedure. This allows us to spot worn parts before they cause costly problemsSource: answers.yahoo.com