Steve is spot on. Otherwise it makes a potentially dangerous situation. Imagine if you suffered a power outage while the spindle was turning 25,000 RPM ............... YIKES! But this is for most machines, not necessarily all of them. I try to make all things default to the safest state but that is subjective too. One thing that might help is keeping in mind that lock out tag out is usually required before maintenance or any type work is done to a machine which means the main disconnect will be turned off. Also, you can typically insure how and when the power is turned on. You can't always control how or when it is turned off.