I would add that there is likely a psychological comfort to having 'enough' rounds to 'not enough' for a situation, and that may factor in your strategy and tactic at the moment.
Consider this scenario. Honestly.
You got home from work later than expected, and rushed straight home for personal reasons. You've just finished chores and packing for your road trip. You're just stepping out to gas up the car and get some coffee creamer or other last minute items at midnight so you can get an early start on your road trip the next day. The gas-n-go is just a few miles away off the interstate. The trip should take 15 minutes, but worth it now to beat the rush in the morning.
You pump your gas and pop in to get supplies. As you are in the back of this medium size convenience store, by the coolers, you see a pregnant woman selecting a gallon of milk from the cooler. It's at that time, you hear the door buzzer followed by some commotion; shouting, and the distinct racking of a pump shotgun. You duck down and can clearly see in the convex ceiling mirror AT LEAST two gang looking young men near the front of the store. One has revolver pointed at the cashier who is frantically trying to open the register. The other thug is walking toward the back of the store with the pump shotgun. The woman is whimpering uncontrollably.
You've been in this store before, and you know that the only exit is several isles over and would be near suicidal to attempt, and you'd be leaving this female behind in rushing for it. She's already in a mild panic and would be impossible to make any coordinated effort with this person.
You have about 5 seconds to figure out your plan before you're 'discovered' by the thug with the shotgun. What will happen if you are discovered? Assault and robbery for sure. Maybe your gun will be discovered? Execution? Worse for the woman? What are you going to do? This isn't about being a 'hero,' but this could be about pure survival.
You are carrying a 5 shot .357 magnum snubnose, which you are proficient with. You have no reloads.
Maybe there's a 3rd guy outside? A lookout? Driver?
Do you flee? Fight? Open fire on one of them for surprise? Open fire on both instantly? Beg for your life?
Go.
NOW- does your decision change if you have a different firearm? Say a pistol with 20 rounds of 9mm? 15 rounds of .40? Or a pistol with 8 rounds of .45? Do you carry a reload? Do you account for gun malfunctions? Misses? Ineffective hits? How about no gun?
Now, perhaps 5 rounds is 'enough' for this scenario. Perhaps not. But you can easily see how only having 5 shots would definitely influence your decision on your tactics, shot distribution, etc. For instance, if you have only 5 shots, you might only put 2 in the closer thug, keeping the 3 remaining for the longer harder shot. You can't guarantee the shotgun works or is loaded, if you can confiscate it. And a scatter gun may not be the best for this scenario because you could accidently hit the clerk. Your OPTIONS open up if you have say 15 rounds of .40 cal, and another mag of 15 rounds on your hip. You might stop the shotgun threat with several shots, and then move on immediately to the guy at the front of the store with several shots, keeping 5 in the mag, and then do a quick mag change and train on the front door....
So, maybe with only 5 rounds, you decide not to engage and roll the dice with being taken captive vs. going on the offensive with 30 rounds at your disposal.