I usually pink all clothing seams when sewing from a pattern. If you use a serger, then pinking isn't necessary because the serger trims and encases the raw edge of the fabric. In patterns, there's usually a nice fat 5/8 seam allowance which gives you plenty of room to pink the edge. if you don't pink or finish the raw edge somehow, the edge will tend to get all messy and unravel after washing. I only have pinking shears and not a rotary cutter. I think shears are easier to pink with because you can trim tight curves as well as straight edges.
Personally, I think you should pink anything that has an exposed raw edge or seam. Otherwise, your seams don't look as neat or finished as they could. Cotton and linen are the worst for unraveling in the wash so you should definitely try to get all those seams pinked.
Personally, I didn't have a pair until a couple months ago when I found a new one at a yard sale. Now, I pink all my clothes and love the finish it creates.
This is exactly when I pink. I use my shears when I have to sew and my serger is just impractical. I also use them to clip & notch curves. It is easier than sitting cutting little triangles out.