From bowiki

This is the technical term for the act of applying a circle of vinyl tape around the edges of the skin. Items stuck to the skin are known as appliques

The tape acts as an absorber and buffer for the vibrations caused by hitting the skin. Only the stronger vibrations are reflected back from the Bearing Edge toward the centre of the skin. The effect of this is to remove a lot of the overtones and harmonics leaving the main Fundamental tone that you want to use.

You will not want to choke the drum entirely by applying too much tape. A certain amount of the secondary overtones contribute to the sound of the drum as a whole and the skill of the maker is in balancing the cocktail of such elements.