It is full of hormones which were powering labour - if you eat them they are extremely good at preventing/stopping PPH as they cause the uterus to contract strongly - they are as effective as the 3rd stage sintocinon injection according to a mw i know.

In addition some hormones drop dramtically after birth in your blood, which is what causes the baby-blues (not PND, feeling wepy and "unstable" about 3-5 days after birth - your progesterone level in the 3rd trismester can be literally 300 times higher than that a few days after birth) and eating the placenta a bit at a time in the days following the birth can really diminish the effect of that progesterone crash (many women have it made into pills or cut into small pieces and frozen for this purpose). Some GP's even treat PND with progesterone creams!

The placenta is also a rich source of vitamins and minerals used up when growing a baby and eating it is a great way to get those minerals (especially iron, which most women need more of following birth) back into your body ASAP.

Plus i expect some people also like how it tastes.

Bx