Why press E-Stop when powering down or on?

I know the power off and on procedure for many businesses is to push the E-stop in before powering off the machine and when powering back on the E-stop release is the last step. Is there a real reason for this or is it just one of those things people do just because somebody said you should?
Unless im mistaking, on most if not all machines the E-stop powers off the servo drives so i can see how that might be a preventative measure for the electronics when the power is turned on.

In most controls, the E-stop first turns off the servo's, and any motors or motion controlling devices, also in the case of those with a traditional PMC/PLC type control before the controller is de-energized, power to all outputs is turned off, optionally the inputs are often left on to enable trouble shooting, if needed.
When powering up, it is considered best for the machine controller software to become loaded and ready before any power devices are activated.
I always conformed to this method in retrofits.
There are rare occasions where the E-stop has been implemented that shut the whole machine off, but not reccomended.
Al.

Also, on some older machines, it also helped by reducing the possibility of back EMF during pump shutdowns. This was especially important on the old Hydraulic "NCs" before my time. And even on some newer machines, it helps to keep the little head drop on mills down to minimum, since the Estop De-energizes the brake before a complete power off.

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