Why we need nipple protector?

Looking for nipple protector. To protect sore or cracked nipples during breast feeding
AVENT Nipple Protectors are made of paper thin, soft, odourless silicone and protect sore or cracked nipples during breastfeeding.
They are butterfly shaped to allow your baby more contact with your breast. Your baby can still feel and smell your skin and continue to stimulate your milk supply whilst suckling, and will return more easily to the breast once your nipples are healed.
Available in two sizes, small (with small nipple - ideal for small and premature babies) and standard. Contains: 2 Nipple Protectors.