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).
If your child takes great comfort from his pacifier, you can let him continue to use it for a while longer. But if your child shows no sign of quitting, eventually you may need to help wean him off the pacifier when he's about 3 or 4.