User blog comment:D.Dragon123/Why Haoshoku haki is useless./@comment-4800978-20130115000804

Haoshoku is just as symbolic as it is powerful. Yes, we'll never see people like Doflamingo or the admirals falling to it's power. But as DP says below, it was used to knock out 50,000 people on Fishman Island. At Marineford it managed to knock out hundreds of Marines and Whitebeard Pirates (which subsequently allowed Luffy to continue saving Ace). Back when Rayleigh first used it at the Human Slave House it took out all the guards and Celestial Dragons, allowing Keimi to be saved.

That alone should say how dangerous it is. It won't knock out the head, but it'll significantly weaken the forces supporting it.

As for the symbolism, it also indicates what a person could become. It shows that while a person may be physically weak now, they also have the potential to become an extreme threat in the future. Just look at the people who could use it; Whitebeard, Shanks, Hancock, Rayleigh - all people who are very powerful and in positions of influence.