One of the most important parts of games involving any sort of combat is weapon balancing. Gamers who frequent the online realms of their favorite games are usually very in-tune with the balancing between every weapon at their disposal, as are those who play fighting games and understand the balancing between each character in the roster. For gaming, weapon balance is key to making the community happy; no one is going to play a game in which someone can gain access to a shotgun that has a reload time of .3 seconds, a fire rate of an assault rifle, and damage output of a catapult using whales as projectiles. Every weapon must have pros and cons, and this applies to both campaign modes and multiplayer, as when there is less of a balance, the game itself suffers as a whole.
For campaigns, weapon balancing is essentially for keeping a game challenging and, at the same time, worthwhile to play. In an obvious example, it makes no logical sense to give the player access to a weapon early in the game that allows them to kill every enemy they see with no effort. There has to be a scaling factor