Professional best practice (REM/Real Ear Measurement) is about precision. It verifies that the RX/Prescription created by the fitting software is the same when the sound reaches your eardrum. Why? Because the RX/Prescription is not always the same (at your eardrum) because people have different shaped ear canals.
But in your case, this extra precision from (REM/Real Ear Measurement) is unimportant. Why? Because your left ear hearing loss has such a profound loss, that the original RX/Prescription is a compromise from the beginning.
