It's not that simple. It actually changes the gameplay just by existing. As soon as a new weapon gets introduced during gameplay the ammo for the gun begins to show up on drops, even if you don't purchase the gun. I picked this up yesterday because I haven't played it in a while and went ahead and ignored the dlc items. Before I even got a quarter of the way between the 2nd and 3rd shop(when the game starts dropping ammo for every gun) every inventory slot was clogged and I was out of ammo for my plasma cutter. Might not be an issue on lower difficulties but it's a big issue on nightmare/zealot.