Very few people hook those up. They are for grounding to the boat or neg terminal on battery. If you are getting lots of static interference they will be helpful or if your boating in a storm.
From Garmin support: Many of the Garmin devices have a chassis ground screw to help filter electrical interference. If needed, a marine-grade copper solid or stranded wire should be connected at the chassis ground and taken to the water ground.1
Bonding a marine device (chartplotters, sounder modules, etc.) using the device’s chassis ground provides some protection to the internal circuits and components from directly induced electrical currents.
Note: Bonding a marine device using the chassis grounding point may not stop or prevent damage caused by a lightning strike.
