[Al_The_Man]

I think there is still some illusion here that some believe that killing the main power will stop all motion, not always so.
A case in point, If I am using say AMC servo amplifiers, these derive their power from one source, the High voltage DC power supply, the internal low level drive logic etc also is powered from this supply, now if I use an e-stop to remove power to the primary of the HV DC power supply, the transformer is off immediatly, but the DC supply is taking time to decay, still powering, to some extent the servo's, now the controller has been shut off at the same time as the AC to the Txfmr. So now the control input signal to the drives, is unpredictable, because they still are under part power, they are still capable of moving (trust me they do).
This is why it is neccessary in many case to also shut the enable off on the drives at e-stop time.
Al.