When women have an epidural, they are confined to bed and are pretty immobile. As we know, the baby’s head likes to be jiggled around in order to get into the pelvis in the correct position to be born. When a woman is mobile, she and the baby “dance” to facilitate the optimal fetal positioning. In bed, not possible. The peanut, while not wiggling mom around or anything, can be placed between her legs in a way to open the pelvis so dramatically as to allow the baby to get into his or her best position to be born.
Watch this youtube clip to get a idea of positions that may help. http://www.youtube.com/watch?v=hSn_BWjL1nw