We find nail polish to be a good enough reason for having them but thought you might be looking for a more scientific answer. We set out to find one by consulting the always reliable Britannica.com.
According to the online encyclopedia, the human and primate nail corresponds to the claw, hoof, or talon of other animals. Human nails protect the tips of the toes and fingers, while fingernails help us pick up small objects and scratch ourselves.
On the other hand, the feet of primates are capable of gripping objects, just like their hands, so their toenails have much the same function as fingernails. However, human toenails seem to be an evolutionary leftover.
We searched the Web on " toenails fingernails" and "toenail purpose." Both of these searches turned up sites devoted to diseases of the nails, which provided more opinions. On one such site, podiatrist Michael Zapf agrees that nails are essential for manipulation and scratching (and he points out the importance of scratching in a primate or human's life).
But the doctor debunks the notion that nails exist to protect the tips of toes and fingers. He argues that your digits wouldn't be especially sensitive without nails. Dermatologist Mitch Bender appears to agree: "People can get along without nails -- toenails more than fingernails -- but they do make daily life a bit easier."
So, though there's some disagreement about whether or not toenails and fingernails serve to protect our digits, our resources all agree that our nails help us pick up little stuff like pencils, peanuts, and even bottles of nail polish.Source: ask.yahoo.com