Summarize:

The breastfeeding nipple shield was designed initially for an infant who is having difficulties in latching, or the act of grasping and sucking the mother's nipples and lower areola area. It is important that the baby latches on to achieve maximum breastfeeding potential without friction or other complications. The breastfeeding nipple shield is can also be used if you have flat or inverted nipples. These sort of nipples make it very challenging for a baby to latch on. The shield also provides protection to the infant in case you have a skin diseases such as psoriasis or eczema, especially in the latching area. Using a nipple shield can help prevent the transfer of any of the aforementioned skin diseases from the mother to the infant. Some professionals believe that you should not use a nipple shield if you are not experiencing any of the problems listed above. They hold that the nipple shield will allow your child to  get used to a firm nipple which may cause the infant to become confused when you try to feed him with your real nipple.  This disorientation that can occur is called nipple teat confusion. The recommended length of time that you should use a nipple shield is generally only 14 to 30 days.
Use a nipple shield if the baby is having difficulties in latching on. Wear a nipple shield if you have flat or inverted nipples. Use a nipple shield if you have a skin infection or disease. Avoid using a nipple shield if your baby is not experiencing any problems with breastfeeding.