Cookies are not only used for tracking purposes; they are also used for content management and customization purposes. Some websites, such as Amazon.com, use cookies to track those products you may be interested in, and deliver content based on those products. Other websites (such as this one) use cookies to store passwords. Sometimes they are used to remember custom configurations for websites.
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How would you like to be recorded what you do on the internet from some low spying company?
Your ISP knows everywhere you visit on the web. ISP's have the ability to tailor content based on your habits also. It's really no different.