If the cord is cut before placental delivery then the exact timing becomes needlessly critical. Too early and the baby isn’t getting enough blood. Too late and the baby might have TOO MUCH blood because of pressure on the placenta in the contracting womb. This could result in jaundice. The obvious solution is to wait AT LEAST until after placental delivery. The placenta might also release hormones and stem cells into the baby during placental delivery which could be important to long term health. And the mother’s body might get hormonal signals conducive to the postpartum process from the baby if the cord is left intact until natural mother-baby separation. We just don’t know, and we don’t need to know. Nature has this figured out already.