These scissors are actually called “pinking shears”.
The sawtooth blade creates a “zig zag” cut.
Why would you want to add a pair of pinking shears to your sewing box?
Woven fabrics fray. Many times, they fray A LOT. Cutting raw edges with pinking shears won’t prevent all this fraying, but it will limit the length of the threads that fray. So, having a pair of pinking shears is handy for trim seam allowances and preparing the edges of some fabrics before your wash them.