Utility is an economic term for a person's overall well-being and satisfaction. Consumers play a role in the economy by maximizing utility, which means allocating their scarce resources, such as limited time or money, most efficiently. Utility maximization is different for every person.
You can start using it right away but it was suggested to us by our midwives to hold off until 6 weeks as pacifier use can mess with their breastfeeding latch (it's a different kind of sucking).
Some people believe that using a pacifier can harm a baby. This certainly is not true. Pacifiers do not cause any medical or psychological problems. If your baby wants to suck beyond what nursing or bottle feeding provides, a pacifier will satisfy that need. However, a pacifier should not be used to replace or delay meals. It may be tempting to offer your child a pacifier when it is easy for you.