Why would you want to dull a nice, sharp nail? When you want to avoid splitting a piece of wood near the end of the board. A sharp nail tip will serve to split a piece of wood if you're nailing near the end of the board.
A tried and true technique to avoid this problem is to to take the nail and turn it upside down and place the head of the nail on a hard surface with the sharp tip facing up. Now lightly take your hammer and tap (yes, here I do want you to tap) the nail tip so as to blunt or dull it.
Now nail into the board and your board will not split. I don't care who you are, that tip is cool!
