In our industry applications E-Stops are used to remove the control voltage to the control circuit. This prevents anyone from issuing a start command either remotely (control room), locally (at the MCC (Motor control centre)) or in the field.
The E-Stop switch is usually also a mechanical latching type switch, that requires you to turn the knob before it will release. Additional safety feature.
The Stop pushbutton is wired in series with the control relay (a N/C switch) and once the stop pb is pressed, power will be removed to the relay, the contacts open up and power is removed from the drive.