To use a pacifier or not to use a pacifier?

I'm just curious what reasons people have for using pacifiers. I was lucky with my baby who never really cried unless she needed something like a feeding so never really had a need for a pacifier. I also have heard bad things about pacifiers and never liked the look of the 4yo still walking around with the pacifier in its mouth but that's just me. So did you use a pacifier and why and would you use it on your next child?