I have utterly no experience of cattle afterbirth. But I'm sharing my twa penniworth anyway
We remove the afterbirth from our dairy goats. In the wild, in nature, they would eat the afterbirth. However, as we now have generations and hundreds of years of breeding these animals to domesticate them, and to change them to what we want, the afterbirths tend to be bigger. The bigger they are (or the more offspring they have- possibly more relative to goats/sheep than cows) the bigger the afterbirth will be, and the more difficult it will be to digest.
So this is why we remove it from our animals. This I guess may apply more to the commercial or dairy breeds of cattle rather than rare (or even smaller) breeds, as we would expect the rare breeds to be closer to their original ancestors, than the ones who have been bred for bulk or milk production.
Beth