When you plug into shore power, the green earth wire connects your boat's underwater metal to the shore earth, and through it to every other boat on the dock. Different metals in the same water, connected by a wire, make a battery. Small DC currents flow, and your anodes, then your propeller, pay for it.
Cutting the earth would stop it and take away the safety of the AC system. A galvanic isolator sits in the earth wire instead and blocks the small DC voltages while still passing fault current. Units come rated 30 A, 50/60 A, 100 A and 200 A to match the supply. ABYC A-28 covers them, and under its revised text a fail-safe unit needs no monitor.
What a surveyor checks
The earth wire traced from the shore power inlet to the isolator, and its label: the rating, and whether it's fail-safe or monitored. An isolation transformer does the same job. The anodes and underwater metal for fast wasting. A boat on shore power with neither is a finding. A boat with the earth disconnected is a safety one.
In the report
"Shore power, 30 A inlet, no galvanic isolator or isolation transformer. Anodes heavily wasted. Fit a fail-safe isolator rated for the supply." See no galvanic isolator.