I speculate it is merely a party trick that only the extremely powerful pirates in the One Piece world can reproduce.
I think that's given but since we've already seen hints at a "rookie" like Luffy performing it, it's going to take a rather important role.
And while yes, it is a useful means of crowd control, like many mysterious plot points in OP, Oda seems to have a 'big picture' use for it. Now, if this means Luffy and the final villain clashing with an enormous battle brewing in the background only to have the two of them knock out basically every pirate and Marine present, so be it. However, although I think Oda will utilize it to that end at least once, I think he has more important plans for it.