Assumption: The hands and knees position prior to labor helps baby move into optimal birthing position.
Studies have shown no evidence that babies move into a better position when moms assume the hands and knees position for 10 minutes twice daily in late pregnancy. This does not mean that there is harm in the position, just that it is not proven to help with positioning. It can and does, however, alleviate backache during labor.
My views: Hands and knees can be a very comfortable position for women during the third trimester because gravity allows the baby to move away from the parts s/he is usually pressing on. 🙂 So, if it feels good to mom, there is no reason not to relax in this position. During labor, this position is particularly comfortable if baby is posterior (facing up). I have not found any studies that demonstrate whether this position can help a baby turn *during* labor. I suspect that giving the baby extra room to move doesn’t hurt as baby is aligning him/herself for birth.