Libraries want to limit the LocalHoldsPriority filling to match only x number of holds in the queue. If there are 100 holds and they want to allow the LocalHoldsPriority system preference to check only 20 first holds for example.
So if there were - 100 holds on the record - the first 20 holds were all for branch A - the 21st was for branch B - Branch B items was checked in you'd want it to go to the first hold for branch A? and then the next time it was checked in would go to branch B as they're now the 20th hold? I can definitely see a use case. My biggest concern is probably tracking down why holds filled in a specific order as this would add a fresh layer of complexity there.