why do you think its an advantage ?
Because it is......you have to stand there like a plank, getting cold, while your enemy screams, shouts, stretches and get's the adrenalin pumping and surging through the body, which aids them and there decision making for the first 10 mins....
If you disrespect the Haka, they get the dander up and spear you...
If you were down the pub of a night, would you stand there like a tool, while some git, jumped around you, eye's bulging, mouthing obscenities....cranking up the pyscholical pressure on you? Would you fcuk......
but they lost