It makes sure that weight is evenly distributed around the entire circumference of the unit.

The common symptoms of out-of-balance tires are uneven and faster tread wear, poor fuel economy, and vibration in the steering wheel, the floorboard or the seat that gets worse at faster speeds.

When all areas of the wheel-tire unit are as equal in weight as possible, the tire will roll smoothly.

This helps it wear evenly, for longest life.