A cookie helps browsers and websites to work together to identify users and prepare customised web pages for them.
When you visit a web site that uses cookies, information about you, like if you sign up for an account, is saved as a simple text file in your browser. The next time you go to the same web site, your browser will send the cookie to the site’s server, which will then present you with customised information on the web page
If a web site does not use cookies, or if you block the use of them on a site, then you will be seen as a new visitor on each page you visit on that site. This would affect you if you were logged into a web site, such as your Control Panel.
At any time, you can clear cookies from your browser, but this would mean that you would need to reset preferences or re-log into a site afterwards.