Permanently Split motors are quite prevalent. Where they fall down however, is with constant stopping and starting. They can't be used on a variable frequency drive, because, by design, it will burn the bearings out over time, with circulating currents. This is why the Induction motor (Cage-type) has become the work-horse of industry. With a VFD, you can have any speed you like, you can ramp up to speed and ramp down again.
