A post processor is a file that contains instructions that are used by SheetCam to permit SheetCam to create G-code that will work with your particular CNC machine. Generally features such as a Floating Z-axis, an Engraver or automatic Plasma Current Control will require a special Post Processor that allows SheetCam to create G-code that can operate these custom/optional features. There are many existing Post Processors that come with SheetCam that contain these features.
If you are using the Floating Z-axis you can download a Post Processor that I have modified specifically for this purpose.
This Post Processor will reset the Z-axis to zero each time, just before the torch fires. This Post Processor also contains a switch offset value to correct for slack in the Probe switch when zeroing the Z-axis. This is set to 0.7mm by default but you can edit the post processor in SheetCam to change this number to compensate for any slack in your own Probe switch.