Some of both
Pacifiers seem to cause a great deal of angst in some, and be a life saver for others.
Babies like to suck, and some really like to suck. For those, unless you want to feed them every 30 min or so, pacifiers are a great good. There is also clear evidence they prevent sids
There is concern that pacifiers given too early can hinder breast feeding
, and weaning off the pacifier
later is not fun.