If you don't reference it, there is no guarantee you are still at the same position you were at when you turned the machine off. At a minimum, you can be off by as much as 3 full steps on the stepper motor, because the driver will always power up in the same (1 of 4) step state regardless of where it was at power-off. Also, the head may drop, due to weight. By far the best solution is to install better home sensors.
Regards,
Ray L.