As far as the research literature goes, there’s not much out there.  Obstetrics is infamous for having little to no scientifically valid research in humans since people are understandably queazy about participating in clinical studies during pregnancy and delivery.  And parturition in other animals models such as rodents, dogs, rabbits, etc. is physically different enough that the details don’t carry over to humans very well.  When I was in my Ob/Gyn rotation in med school, I asked some Obs just to get their opinion and the general feeling was that there was probably not much contribution from the decompression.  One Ob conceded that maybe in difficult deliveries where there was risk of prolonged hypoxia, theoretically there could be benefits to decompression.  I think that without an actual rigorous study, we are left with speculation and anecdotal evidence.