I guess everyone has their own perspective on this.. here's mine:
I was very anti-paci with my first daughter. I never wanted her to get addicted to it so I offered it once or twice and she spit it out and I was glad that I didn't have to deal with that whole issue. With my second daughter we tried it again, my husband tried it more rigorously and she took it and it was amazing! It took her a few weeks to figure it out and then she would only take one certain kind. Then I realized, she was self-soothing. I had this huge epiphany about it and regret not trying a little bit longer with my first -- she to this day still has a problem self-soothing and I really relate it to this!
We are on our third baby now and he too needed some time to learn how to use it. I never had any nipple confusion or anything like that~ We started from day 1 and just kept offering it until he figured it out. He prefers a certain kind as well. I give it to him when he needs help being soothed, so if we're in the car and he's crying a lot, but I can't get to him, I offer it. And as montessorimama said, after nursing when he's falling asleep (although sometimes this can be a little tricky bc they obviously know it's not a booby anymore).
As they get older and become vocal, start only offering it at naptime and bedtime and encourage communication as a self-soothing technique. My daughter used her paci at night until she was 1 1/2 (which was longer than I intended, but perfect for her). I'd be weary about finger sucking because that's a harder habit to wean.