I think if you can get away with that kind of defense there could be two advantage in keeping your hands down. Presenting a smaller target and faster head movement as less weight is on the top.
RJJ fans, makes it look like your clowning the other guy, you're showing your superior handspeed and flexibility in a showboating way and saying, "I'm so fast I don't need a high guard"
That style is stupid, it's how sergio got dropped on his ass by pavlik. even a prime roy put his hands up in guard when he needed to.
I would think some of it has to do with rhythm. When people dance their body parts are situated in unique ways. Maybe Sergio feels he develops good rhythm by having his hands down while feinting and moving on his feet.
I've always thought this. Beginning boxing at 20 is really late, so he probably just used what worked for him.
Not the reason, but a major advantage, especially at his age: It saves and incredible amount of energy. Try holding two 10 ounce cans up in front of your face, for just 3 minutes. I mean, actually do it. It's a lot harder than you might think. Now do it 12 times, while dancing around. Guys who have never actually boxed have no idea how hard it is. This style is one of the reasons Sergio can still compete at such a high level, even at 37.