...whoops, just realized I forgot to specify!
So this is British-specific but other countries would have had similar concerns.
Their Enfield (rifle musket or carbine) drill was focused on how they used it as a sharpshooter weapon for everyone in the army. There was no "fire" command in the drill book, just "present" and then the soldier decided for themselves when to fire - like a hunter, they picked their moment because you can't keep the rifle "on target" at all times when shooting at long range.
When the Snider came around, though, rate of fire quadrupled. A 70-round ammunition pouch that had previously lasted half an hour would now be expended in about seven minutes, and furthermore there was a tendency noticed in many countries for troops with breechloaders to do what the Prussians called "Schnellfeur" - as soon as they're told they can start firing, they do so and don't stop until they run out of ammunition. This is partly a failure of drill and partly psycholgical - it feels like you're doing something, and what's more once you have fired off all your ammunition you clearly need to resupply and in the interim can stay in cover with a guilt-free conscience.
As such, the doctrinal focus changed entirely. With the Enfield, a soldier could not fire very often and as such needed to start at very long range to get a useful number of chances at a target, as well as not producing much smoke; with the Snider, a soldier who started shooting at maximum rate at an enemy at 700 yards would run out of ammunition by the time they closed to 100 yards or so, and what's more they'd have been firing the last sixty rounds into a fog bank of their own making.
So drill included the "fire" command again, this time as a method of regulating ammunition consumption. The best shots would fire independently, but with only a few of them they wouldn't create too much smoke, and if a target deserved a volley at range it would be commanded by the officer/s. As the enemy got closer, the unit would plan to unleash a short, vicious barrage of close ranged rifle fire, one of such magnitude that it would cause the enemy to break and run as well as probably killing quite a lot of them.
This is almost certainly what was done at Isandlwana - the Zulu met a wall of Martini-Henry fire at close range and just kept coming, probably by outflanking with their bulls-horns.