What is the primary purpose of the rubber or vinyl handgrips on most pliers?

The primary purpose of the rubber or vinyl handgrips on most pliers is to protect users from electrical shock. Handgrips made from these materials provide electrical insulation, which is crucial when working with live wires or electrical components. This insulation helps prevent direct contact with conductive metal parts of the tool, reducing the risk of electric shock during electrical work.

While comfort, grip strength, and appearance might be secondary benefits provided by rubber or vinyl grips, the key function is the safety it affords the user when operating the tool in potentially hazardous electrical environments.