Vests, Jackets, Lined Skirts and Trousers. Pinking shears are useful for finishing these seam allowances that don't take any stress or wear and tear. Pinking keeps them from fraying without have to zigzag or serge and risk those stitches being visible on the outside. You can also use pinkers on unlined garments, provided the fabric isn't too loosely woven or too likely to fray, though I admit that for unlined garments where the seams are more exposed, I'm more inclined to finish the seam allowance in neater fashion.
Some will say pinking shears aren't a necessary sewing notion, and others will say they can't live without them. For me, pinkers are nice to have, quick and handy to use (especially if the serger's got the wrong color thread in it), but not earth shattering if you don't have a pair.