Relief Cuts - What are they for?

Relief Cuts in Flooring

These small cuts out of the bottom of flooring actually have 2 purposes.

Firstly it breaks the tension that causes wood to cup. (Cupping is when the board becomes curved across the width of the flooring).

Secondly it cuts the surface area that contacts the sub-floor. If the boards were flat on the bottom they would likely have more creaks and pivot points. Small bits of sawdust, grit or sand may cause the flooring to pivot or not sit flat after if the relief cuts did not exist. Cutting the surface area down increases the pressure on the contact points--enabling more solid connection.