By default, I don’t put any cookies on your computer. However, if you click Set Cookie I’ll give you a User Number. This cookie will last until you decide to click Clear Cookie to remove it – or about fifty years, whichever occurs first! (Or of course you could remove it by other means if you prefer.)
This would help me understand how people use my site, and hopefully enable me to improve it, by letting me track which pages are accessed by the same user, and how they navigate from page to page.
Whether you have a user number or not makes no difference to your use of the site.