I added it because it wasnt homing the Z access or using the probe. It just started the print in mid air from the position it was in after adding filament.
I opened the same file in Cura and noticed the extra Z0 and pasted it into S3D.
For anyone that is having issues with the probe/ levelling on their printrbot metal... Remember to add Z0 to under "scripts" in FFF settings. By default its: G28 X0 Y0 ; home X and Y axes G29 ; probe Z It should be: G28 X0 Y0 Z0; home X Y and Z axes G29 ; probe Z I just picked this app up ...