Arguments in favor
Many birth attendants still practice the artificial rupture of membranes, more commonly referred to as breaking your bag of waters. There are several reasons for this. For one, labor tends to go much more quickly after the bag of waters has been broken. Doctors and midwives usually use a special device called an amniohook for this. Breaking the bag of waters is actually used as one of the methods of labor induction. The other reason is that meconium stained amniotic fluid can be an indication of fetal distress, and lots of birth attendants want to take an active approach and know what is going on. Additionally, when the waters break by themselves, they can "splash" in every direction. You can't really blame your OB for not wanting to be covered in your bodily fluids!
Breaking the bag of waters early on in labor does have disadvantages. For one, if they are broken before you have regular contractions and labor does not then proceed according to the hospital's plan (often 24 hours are "allowed" for labor), the risk of infection increases. That is why, when you don't have regular contractions when your membranes have already (been) broken, it is possible your health care provider will want to augment your labor with drugs like Pitocin, and your risk of having a cesarean section also goes up. Breaking the bag of waters early on also means your baby will not be able to get into optimal birth positions if they were not already there. Some fetal positions are more ideal for vaginal birth than others. And, besides that, breaking the waters means the odds of the umbilical cord slipping out before the baby go up. This cuts off baby's oxygen supply and is very dangerous.