It has been argued that sleeping with your nursing baby increases nighttime nursing and that this causes dental problems such as milk decay. A baby usually only wakes up if he or she is hungry to eat. Even if the parent falls asleep while feeding, the baby stops eating when full. The suckling that some babies continue to do at the breast does not cause milk to leak. The baby simply is not drawing milk out.
Nighttime nursing is much easier on the parent when they are sleeping with their baby.
Both wake up much less during the night and the parent is not on edge listening to see if the baby is alright because he or she is with them in bed. The argument that co-sleeping deprives children of the chance to learn how to fall asleep on their own is debatable. If anything, babies sleep better with their parents. Their sleep cycles synchronize with the parents' and they tend to fall asleep at the same time each night. People argue that co-sleeping interferes with the baby developing a strong sense of independence and becoming a separate person.