In conjunction with System Shock 2 following in the first game's footsteps as far as energy weapons using an energy supply instead of ammunition. System Shock 2 is very deliberate about the progression from hoarding limited resources to spending them relentlessly because nearly everything justifies them and you have plenty to spare, and it's actually one of the better-executed aspects of System Shock 2's experience. The latter case is almost understandable to me. The two most egregious examples: the leveling mechanic alongside the inventory system, and the limited ammo alongside the weapon durability system.
Raising the question of why have both systems at all?
One of the more frustrating aspects of System Shock 2's (mis)use of RPG elements is how there's multiple cases where multiple separate systems primarily serve to produce.