From Wikipedia:

Some polydactyl kittens initially have more difficulty in learning to walk and climb than normal animals. However in some cases it appears to improve the dexterity of the animal. For example, a common variation of polydactyly with six toes on the front paws, with two opposing digits on each (comparable in use to human thumbs), enables the cat to learn and perform feats of manual dexterity generally not observed in non-polydactyl cats, such as opening latches or catching objects with a single paw.