Well, you're not very likely to hit them. Certainly at, say 100m you're chances of hitting while on full auto are a LOT lower than if you were firing controlled bursts. Even at 25m I'd bet on the controlled bursts guy. Even if you're shooting into a crowd, sustained automatic fire is very wastefull because many of those bollets will go into people you're already hit enough, whereas with controlled bursts you'll make more efficient use of ammo and thus actualy slot more bad guys.
Hmmm, maybe you're thinking of the scenario where there is one guy with an assault rifle, and one guy standing 30 yards away. And perhaps you're right about that. That one guy standing 30 yards away is more likely to get killed if you can specifically target him with a controlled burst of fire than if you just fill the area he's standing in with lead bullets.
On the other hand, if you have a bunch of guys 30 yards away, and you want to kill as many of them as possible, then automatic fire seems like the better option. That seems more in line with what I've read about World Wars I and II, and my experience in Squad Leader when I took a platoon across the street and it didn't make it. As explained by the guy who was teaching me the game, he explained that maybe two or three guys would have made it across the street.
I also remember that archers can also set up essentially area of effect fire; when a unit of archers is defending an area against a unit of infantry or calvary, the archers can just fire into the attackers, making life for any specific attacker dangerous.
I also remember a situation where a player running a radio expert PC wanted to fire at a mob of zombies 100 feet away. I am aware that a pistol would have almost no accuracy at that range, but the house rules I was using would have a significant chance of hitting one of the zombies in the mob
other than the one she was aiming at, since there was a whole mob of them. I guess that seems reasonable, that even though Zombie X was probably safe, it wouldn't really matter as long as one of the zombies got hurt.
(Of course, hurting one zombie in a mob of zombies might not be the best combat tactic for that situation. I guess it was a good thing that the character was a radio expert and not a military tactics expert.)