This information can be easily integrated into the store of information the site already has about sessions and repeat visitors. Much of the value perceived by businesses of the Web is in advertising revenue. Many sites have decided not only to collect users preferences but also personal information, like names and other contact information. Demographic information is especially valuable, so some sites ask about the age, gender, and income level of their users. The sales data ecommerce sites collect is also usually integrated into the site's user knowledge base.
Some companies leverage cookies even more.
But you could be wrong. As was previously mentioned, advertising is an important source of revenue on the Web today. Many sites carry advertisements in cooperation with companies who specialize in placing ads. Many users may not have realized that the contents of a web page can be assembled from multiple servers, and that advertisements are often delivered directly from an ad company's server, rather than from the server that provides the rest of the page. This gives the advertising company the opportunity to set its own cookie and keep data about which ads have been served to a particular user visiting many sites.