Found this article...
"Single-phase induction motors drive many arbor-mounted cutting tools in the home workshop. Stationary grinders, table and radial arm circular saws frequently turn abrasive or cutting disks that are directly mounted on the motor's spindle. These disks have large inertial moments that allow them to free wheel for a long time after the power is turned off. A lengthy coast to complete stop often amounts to a major inconvenience."