Hey Matticustard, hey Ryan @PaquetteWoodworks,
Just in case someone is interested in the subject, I tried to explain this in the thread mentioned above
In fact you need both. What Ryan refers to is if there is something to abort quickly and stop all running motors, e.g. to avoid harm to humans (or animals), but without cutting power to everything. In fact VFDs with spindles running on them don’t like sudden power cut at all and can even be damaged. However what you always should have too, is an emergency switch preferably at the entrance of the room, with which you can safely cut off power on all hot lines for the entire room, for the case of fire.