I just yesterday watched a video where a former Delta team leader was talking about how much ammo does someone need. Boiling down a much larger presentation, he concluded that you should allot three rounds per adversary unless your role is suppressive fire in a military/battlefield context.
The mood of his video was really "If you start feeling like you need tons of ammo, maybe it's time to hit the flat range to make sure you don't suck at shooting."
I watched something similar. The Operator made reference to "The rule of 3", he went on to say most defensive shootings contain 3 shots fired within a 3 foot radius and occur within 3 seconds of the encounter.