So we can personalize our pets. Everyone has his favorite pet (but they may not have the stats we need or desire). Some pets are school pets (we love the pet looks but not the sttats).
example: put rescue rover (ice) body over my max healing piggle pet. It would act like rescue rover, but have the stats of the max healing piggle pet. Restrictions: Can not be hatched with, unless original pet is unstitched. Pet stitching is expensive 1k+ crowns, but cheap to unstitch 100 crowns. When KI comes out with a new pet, but we don't want to start from scratch, or its the wrong school. so we can stitch it over one of our existing pets. If you hover over the pet still says piggle pet, because the stats did not change. same as when you stitch over malistaire gear, because of the gear's stats.