RE: 6.4.0-RC Firmware for Prusa CORE One
The X/Y axis are homed first and move to a position over the bed itself. The Z moves up until the nozzle is sensed, then it raises, moves to a position over the corner of the bed (testing a bed is there) and raises again. IF it misses the bed - it fails and wont proceed until it is homed properly and senses a bed. Automatic homing is perfectly safe. Try it..
Oh right, the firmware moves the bed down first, then homes XY, then Z. Then indeed my first concern is not an issue (except for the very minor chance of crashing the bed into the bottom end stops during the initial brief movement downwards).
But having any object, and in particular the prior print, still on the heatbed does make homing unsafe, right? So I am still not sure whether I would want it to happen automatically when I power on the printer, which I understood to be your suggestion.