It's more for throttle response...unless your getting a good deal on it, the money could be spent more wisely elsewhere. I did it to mine cuz I found one on a junked Altima for $30. I can't really tell if there was a difference, because it was installed along with some other modifications....
It will help, but how much and if you'll even notice it, I can't really tell you.
Just a 5mm larger TB on a stock alty, you won't feel shit.
But the more exhaust and intake mods, you should feel a little, in throttle reponse like Peterson suggested. True the money could be better spent elsewhere. But if all bolt ons are on, and you're squirtting Nitrous, then it will defiantely help. Otherwise, i wouldn't bother with it.
Also, read the other topic about this. I posted some helpful info on applications.