Occasionally we do a fun sparring drill where one person has to spar with his hands down and rely on head and body movement for defence.
The defensive side of things with your hands down is hard, no doubt about that. Naz's footwork, angles, shoulder rolls, body and head movement was otherworldly. That's how he could pull it off at the highest level.
Now the advantages of boxing with hands down is your punches are much harder to see because they originate outside your opponent's peripheral vision. And because the fist is travelling further, with the right body mechanics, it's possible to generate great power. Now because the fist is travelling further, you need speed to be able to make it effective. that's why just about all boxers who fight with left hand low, using the shoulder roll for defence have great speed. Floyd, RJJ, Joan Guzman are just a couple of examples.