Noise

Laminate flooring that has no padding will often produce louder sound when walked on than padded flooring. Wood laminates react just as any wood product, producing echoes that reverberate against hard surfaces.

Comfort

Padded laminate flooring creates a softer surface to walk on. The padding allows the flooring to give when pressure is applied, cushioning the force of the body weight as a person walks across the floor.

Moisture

Many padding products for laminate flooring include a vapor barrier. Although laminate floors are sealed tightly in their construction, moisture can still permeate to the sub floor. Some padding for laminate flooring is made with air pockets built in, which act as a sponge to absorb moisture and disperse it to the sub floor where it can evaporate.

Floor Life

Padding can prolong the life of laminate flooring as well. The cushioning effect allows the flooring to give as it is walked on, preventing uneven pressure on the wood laminates that can eventually stress certain areas of the flooring.

Floor Surface Leveling

Many sub floors will become uneven over time. Padding that is applied under laminate flooring can help to bring the sub floor and underlayment to an even level.

Source:

Installing-Laminate-Flooring.com: Vapor Barrier