If you want to share a page through the share box on the left that will undoubtedly drop a cookie on your browsing device to show you you've done it. If it didn't, you couldn't be sure you'd done it when you revisited the page would you? See? They really are harmless little creatures who only need a nice warm hard drive to sit on. But if you want to know more about cookies, how to stop them or get rid of them, try this link.