Genuine question but have you ever used a gas iron ?
rubber ring - end of the tail slowly dies, discomfort last for a while with the ring on, and they run about for a bit with a rotting dead bit of flesh hanging off them. Also leaves rings all over.
gas iron - about one second of pain, tail is removed, wound is cauterised, job done. Lambs straight on their feet and run off to eat.
Also practically speaking - running mobs of 250-400 twins and 300-1000 singles, catching them up and ringing as you go is nigh on impossible, due to lambing rate, plus causes a lot of miss mother