Recently I was at my British reenactment group and I heard one of the members describing the role of light infantry and skirmishers in a way that seems very accessible to even those without any sort of military background or exposure. So, I present it here, lifted and with no claims that the work is mine.
Think of a cat prowling in a dark wood. It’s so dark out that even with its good eyesight it can barely see in front of itself. In cases like this the cat’s whiskers are critically important. Fanning out to feel and disturbances and immediately convey that information back to the brain. That is the role of the light infantry. They’re out there to see what’s out there. Even if the whiskers stumble upon a mouse, it’s not their job to snatch it.
If the brain (the commander) decides to attack what the whiskers have found, that’s when he sends in the teeth (and, perhaps the claws). And here’s where the grenadiers come in. These are the shock troops designed to tangle with the enemy first under the assumption that they are the best trained, disciplined and less likely to break. Of course, as the modern age of warfare was approaching and mixing with old notions of what battle should look like, this meant that grenadiers typically took more casualties than their ‘regular’ peers.