It's a good question, because an okay-armed gang attacking an okay-armored gang (say, 2 harm versus 1 armor) will only deal 1 damage every time harm as established is dealt, and it doesn't sound like much.
But over four rounds, that means the defending gang is taking, say, a maor injury every round, and then there are the several people who take a minor injury, and then another, and then another, without an Angel (or equivalent) and crew patching folks up here and there... to me, seems quite like 1 harm can add up, all else being equal.