You have to line up musket troops to give them orders too. There’s no radio and you have to shout over the noise and smoke.
Remember, these are black powder guns. They’re loud. If your troops are right next to each other you can more easily direct them to fire, advance, or retreat. Advancing or retreating quickly can take advantage of enemy weaknesses and break up the opposing army. If your guys are spread out, you can’t tell them anything.