To tell you when to get out of the bath, according to my mom. But that's not good enough for science!
Kyriacos Kareklas and Tom Smulders of Newcastle University in England noted that the wrinkling of skin is actually controlled by the nervous system. Cut the nerve and the skin of your fingertips actually won't wrinkle. So, there must be a function to the wrinkle, right?
So the two decided to do the experiment and discovered that wrinkled fingers help improve the handling of wet objects: