At our dairy we also take the calves away straight after they're born, within 12 hours. Many dairymen choose to leave the calves with the dam for the first five days, since the milk the dam gives for the first five days is still basically colostrum and unfit for human consumption - in other words, it can't be sold, so the baby might as well drink it.
From a financial point of view, it more or less makes sense, but in our experience the cows and calves suffer from terrible separation anxiety if their bond is allowed to strengthen over the five days. Removing the calf so early prevents any real bonding from taking place and very few cows and calves will pine for each other when they're taken away that quick. Also gives you a better opportunity to monitor mother and baby for illness.
With the old Jersey cows who are prone to milk fever, we'll sometimes refrain from milking them out for the first day or two, to keep their calcium levels up a bit. Also something you can't do when she's suckling a calf.