I knew I had seen this somewhere. its in the manual for the Ever Last 205 pro
"The ground bolt on the rear of the machine is designed to help eliminate High Frequency interference from the machine. Ground the Case bolt to a separate wire to a metal ground rod outside the facility that is in moist soil. Occasionally multiple ground point are required. DO Not ground back to the electrical circuit ground as harmful HF feedback can occur. Do not attach HF ground directly to table, cart, electrical circuit of panel box!"

That adds more confusion