That was the tactic of the day, mass volley fire and even when they were only about 50ft away from each other, a load of the shots would still miss, solders were trained to stand shoulder to shoulder, it really was the only way to get kills with the smooth-bore musket, the British at the time were using the Brown Bess musket and could normally shoot 3 rounds a minute if not 4, most other army's of the time could mostly only manage two.
Now I know the British lost the Revolutionary war, but to begin with the American forces were having a lot of trouble fighting the British at the beginning of the war, because they were using the same tactics, I think it was taught to them by the french and they were being out shot, but that said near the end of the Revolutionary war when Britain was losing this was mainly because of the distance involed for surpplys, men, etc and a change to American Tactic, they used alot more gorilla tactics like hitting supply lines, reinforcing troops.... etc, so when the final battles came the British were that weaken they couldn't stand so loss the war.
As for the tactics changing, well I can't speak for the Americans, But I know they were still using the tactic during the civil war, but the British started to change tactics around the time of the Zulu wars around 1879, with the introduction of the martini henry rifle, which was no longer a smooth-bore musket, but a proper rifle with rifling and a cartridge bullet (still using Black powder), this meant they were a lot more accurate and the need for mass lines of men firing volley shots were not need anymore.
Also finally when the Boar war started in South Africa in 1899 the British finally got away from wearing the red coat and changed to a light brown jacket, this was because of the improvement in accuracy in rifles and standing out like a sore thumb in the red jacket.