Even in a war, if you are properly trained, spray and pray is never really a solution. As a Marine, I trained my boys that if you're not aiming at something, then you're not really suppressing anything, now are you? Suppressive fire also does not mean 'expend all rounds'...no, it means you put the appropriate amount of rounds downrange to fix the enemy in place and to make it really difficult for them to leverage effective fire at your maneuver element. If you don't see something or aren't aimed in...don't shoot. You have to watch your ammo levels even closer in an extended firefight...don't think I'd ever want to be caught with my pants down.
Now, I won't say that there weren't times when a few machine guns weren't laying down walls of lead in order to do that, but all in all, every man is accountable for every round that leaves his weapon.
In modern times - knowing what we know now of tactical employment of personal weapons systems and movement, fire, cover, concealment - I don't believe there is ever
reallyan appropriate time for spray&pray. You do not fire unless you have PID, you do not fire unless you are aware of what's behind the target, and most importantly, you do not fire unless you know what you are shooting at.
If you're clearing alleys and such....well we have handy little things called grenades, which work exponentially better!