Please don't duplicate. Please, please, please. Duplicating means you don't want to play the game. The guys that duplicate show up and say, "Hey, can I get a piece of cobblestone? I want to duplicate it to build my house." O.o The day they don't get their cobblestone free, they leave the game and never come back. OOOOOmg. Even they guys that say, "Oh, I only duplicate my diamonds," they aren't playing anymore.
Wait! I know a legit reason to duplicate! You can duplicate the pieces to put back into the game after the griefer that duplicated the TNT left...LOL j/k