A saucier is not the same thing as a sauce pan?, although it IS a pan for making sauce. And you can use it for just about anything you'd make in a sauce pan?. That's why I prefer a saucier to a sauce pan? if I am forced to make a buying choice.
The thing that makes a saucier so very good for making sauces is the curved bottom edge of the pan.
Attach:saucier.jpg Δ A saucier is much more gradual in the transition from bottom to side, which allows a whisk? to do its magic in the corners, breaking up lumps and mixing everything while keeping all from burning.