It doesn't, it helps you hit harder Ebs or hit people who are bigger. Also makes it harder for people to hit you
Technically, it can go up to 3% plunder and it's the blue bird trinket thingythe boots for part 3 also have a plunder bonus, but for pvp and it ranges anywhere from 0% to 10% depending on what level it has been upgraded to, and what tier you get from part 3.