Babies and pacifiers. What is their purpose and are they really needed?

I was wondering what the point of a pacifier is? Is it just to keep a kid quiet? Can you not give a baby a pacifier ever in their life? They just have to be weened off them anyway. They get conditioned to sucking on something nd might start a habit of sucking on their thumb when you take a pacifier away. That can cause teeth problems. Would it be a good idea to not give a kid a pacifier? And with that same idea, could you not give a child a bottle at bed?