A trainer used to tell me to do it sometimes because you ram the jab out with more behind it and it's straighter that way. That's all i was told by someone who knew what he was doing personally
I sometimes employ it for me it makes me looser for head movemnt and out side boxing. I dont think it protects the body much better as i feel i can go into a sort of shellthat defends the body better. Also the jab you throw come from undeneath your opponents vision and is harder to see coming.
Also because the punches travel a longer distance with a low gaurd you can produce more power with both hands. Mass + Distance + Speed = Power.
As Sam Langford said, the head has eyes. You can make better use of them if your own gloves are not covering them.
The biggest reason is for baiting purposes. Opportunities to counter a punch on a seemingly open target. You have to have good reflexes and be a good judge of distance. You'll notice that many fighters who keep their hands low bring them higher the closer they get to their opponent. I just think its a baiting thing mainly. Guys only do it when they're in with someone they think they can outspeed or have faster hands than, like to counter or lead. I watched Mayweather-Judah last night and it was the same thing- low hands until they got close and once it became obvious Judah can match his speed, Mayweather kept a respectfully high guard. He hasn't done that in a while. He mainly does that high left shoulder **** even in close nowadays...
I think a good argument can be made to support hands down when it comes to exceptionally gifted athletes like SRR, RJJ etc...These athletes were unusual and once they aged they had no defense for other good athletes. No fundamentals like hands up, chin down bobby and weaving and blocking punches. Good post and great question IMO this is an individual ability based off of the fighter not an assembly line style.
While watching footage of a bout between Tommy Loughran and Mickey Walker, I noticed that Walker had a very tough time hitting Loughran throughout the bout even though the latter almost always held his hands at waist-level unless he was throwing punches or clinching. If someone can that while facing an all-time great, who can say that it is the wrong thing to do at all times? - Chuck Johnston
While watching footage of a bout between Larry Holmes and (Snipes, Shavers, Norton, et al.), I noticed that Larry Holmes got tagged with right hands. Using his greater abilities and fortitude he won. He chose to fight as he did and his record speaks for itself.
I used to box competetively as an amateur and still box to keep in shape..heres my take..a low guard is more comfortable to move with less rigid than high...everything in the body seems to flow better with it low...more of a range of movement available and quicker options..but i can appreciate the flaws of the style....its what suits the individual.