Many machines are wired the same way a light switch is set up in your home. You turn on the light and it stays on until you turn it off, it burns out, or it loses power. We do not mind if a light turns back on after a power outage, but we certainly would not want a dangerous machine to do the same thing.
Anti-restart protection means that a machine will not start automatically by itself without human intervention. You would not want your drill press to start up by itself, would you? What if someone decided to remove a drill bit and then the power came back on all of a sudden? In addition, if a guard is opened while the machine is running, the machine will not restart when it is moved back into a safe position. The start button will have to be used to restart the machine.
Example of a Bench Grinder with Guards and Anti-Restart Protection:
Another common machine that is often left unguarded is a lathe. We often supply Chuck Guards, Chip Shields and Anti-Restart Protection for lathes of all sizes:
An additional safety device that should be considered on lathes is the lead screw cover. These expand and contract to keep the spinning lead screws covered and your operators safe from entanglement: