Cookies are small data files which are downloaded onto a computer when a website is visited for the first time. They store information about the visit to the site so that the next time it is visited, the site knows that a user has been there before and can tailor the experience. The computer facilitates this by checking if it has stored a relevant cookie and, if it has, sends the information stored in the cookie back to the site.
There are privacy implications flowing from their use.
To eliminate irrelevant aspects of the site for routine users and store information for an easier and more tailored experience.
The nature of cookies is that they are data retainers. One-off data retention seems relatively harmless; however, it is the cumulative effect of data retention which have implications for personal privacy.