According to narrator, having double the amount of arms and mouth is a huge advantage for curse sorcerers because
1, they can make signs while still having two spare hands
2, they can perform incantations without interruption
Using this body and his two weapons, Sukuna destroyed all his enemies 1000 years ago, and also defeated the Black Pacification Squad( angel, elites of Abe clan and the remaining members of the Sugawara clan)