Pros of Dummies;
They do help to soothe if baby will take one.
They can be helpful as a comforter when someone else is looking after the baby.
Can be useful for a quick comforter when you can't do much else, in the car or in DC's school play for example.
My DC have all made a really cute 'mmmm' noise when the are tired and settle down with a dummy for a cuddle.
Cons of Dummies;
They are easily over used.
They are a pain if DC has a blocked nose, and can cause a slobber rash when teething.
Annoying if lost at night, I dread the clatter of a dummy falling through the cot bars.
Can be a problem to quit, although DD had one unsettled night then wasn't bothered, and DS1 decided for himself he didn't need his anymore.
You will get some people calling it a dodie.
Some people think you are mad not to use them others get sniffy if you do use them.
As someone who thumbsucked until 19 and pregnant with DC1 I would rather have had a dummy as a baby.