When you select a campaign, you also get to select some game mode settings (the bit with network play options). One of the options here is to enable infinite ammo - which is available in offline and online modes.
What does this mean? Can you use infinite ammo any time, or does this mean you can use an "infinite ammo" unlock reward once you have it? And more importantly, are there any disadvantages to enabling this mode? (e.g. prevents trophies, prevent completion progress)