Cookies are designed to assist your computer or device to remember something the user has done within that website e.g. remembering that the user has logged in, or which buttons have been clicked.
There are specific cookies related to knowing a user is logged in or not. These are known as authentication cookies. Authentication cookies are important for the website to know what information to show you, or if it needs to ask you to log in.
If you wish to find out more about cookies, we find this website quite helpful www.aboutcookies.org