I had a situation where some NPCs that were PC allies were fighting a monster. The monster would kill one now and then, and part of the PCs goals was to get to where they could intervene ASAP. I didn't play out this fight with the rules. An NPC just died every round and whenever the PCs fought the monster whatever its hit points were was whatever they had to deal with. Whatever damage the NPCs did before that was show.
That's exactly the kind of situation where I would want to use actual rules to see when NPCs die and if they deal damage.
I suspect my players would be annoyed at a regular pace of 1/round and the NPCs doing no damage. That would mean they couldn't try to protect the NPCs with a spell like circle of protection or boost their fighting ability with bless. There's also the question of whether the NPCs that go down would be dead or could still be healed, but for that I already use house rules.