Many cookies are benign and are designed to save you time. For instance, our bulletin board, The Info Exchange , writes six cookies to your hard drive and stores your username and password so you don't have to type it in whenever you make a post. Nothing else is stored on our server that isn't required of your registration for posting. Most websites who use benign cookies ask you if you want them or not and leave it up to you whether to accept them. This is good policy.
Malignant cookies are a different animal altogether.
Since the server is recording which pages it sends you, this data can be mined with the intent of developing a profile of your interests. As you re-visit the site, your profile is updated with any additional information the server can gather. If you fill out a form, it might save your name. If you sign onto a mailing list, it might save your email address. If you order something, it might keep your address and credit card info.