Here's some stuff that I've recently learned about browser cookies. Most of it came from a site called 'about-Tech', part of the 'about.com' world. Because it is not mine, and I have no idea about how long it will be available, I've copied some of their stuff to present here. I'll put all of the links to their pages at the bottom of this, so you can read through there original stuff. But, know that a lot of their pages include videos that start automatically and may be loud. So, here we go.
Cookies are very small text files placed on your computer by a Web server when you view some sites online (not all Web sites place cookies). They're used to store data about you and your preferences so that the Web server doesn't have to repeatedly request this information, potentially slowing down load time. Cookies are commonly used to store personal registration data like your name, your address, the contents of a shopping cart, your preferred layout for a Web page, what map you might be looking at, and so on. Cookies make it easy for Web servers to personalize information to fit your specific needs and preferences when you're visiting a Web site.
There are different explanations for where cookies got their name. Some people believe that cookies got their name from "magic cookies" which are part of UNIX, an operating system. Many people believe that the name originates from the story of Hansel and Gretel, who were able to mark their trail through a dark forest by dropping cookie crumbs behind them.
The easiest answer is that cookies, in and of themselves, are completely harmless. However, some Web sites use them to track users as they browse the Web, collecting highly personal information and often surreptitiously transferring that information to other Web sites without permission or warning. This is why we often hear about Web cookies in the news.
Because cookies are simple text files, text files cannot execute programs or carry out tasks. Nor can they be used to view data on your hard disk, or capture other information from your computer. Furthermore, cookies can only be accessed by the server that initiated them. This makes it impossible for one Web server to snoop around in cookies set by other servers, grabbing sensitive bits of your personal information.
Although cookies can only be retrieved by the server that set them, many online advertisement companies attach cookies containing a unique user ID to banner ads. Many of the major ad companies online serve ads to thousands of different Web sites, so they can retrieve their cookies from all of these sites, too. Though the site that carries the ad can't track your progress through the Web, the company that serves the ads can. This may sound ominous, but tracking your progress online isn't necessarily such a bad thing. When tracking is used within a site, the data can help site owners tweak their designs, enhancing popular areas and eliminating or redesigning "dead ends" for a more efficient user experience. Tracking data can also be used to give users and site owners more targeted information or to make recommendations on purchases, content, or services to users, a feature many users appreciate. For example, one of Amazon.com's most popular retail features is the targeted recommendations it makes for new merchandise based on your past viewing and purchase history.
This is a question that has different answers depending on how you want to use the Web. If you go to websites that personalize your experience extensively, you won't be able to see much of that if you disable cookies. Many sites use these simple text files to make your Web browsing session as personalized and efficient as possible simply because it's a much better user experience to not have to keep entering in the same information every time you visit. If you disable cookies in your Web browser, you won't get the benefit of the time saved by these cookies, nor will you have a completely personalized experience. Users can implement a partial stop on Web cookies by setting Web browsers on a high sensitivity level, giving you a warning whenever a cookie is about to be set, and allowing you to accept or reject cookies on a site by site basis. However, because so many sites use cookies these days that a partial ban will probably force you to spend more time accepting or rejecting cookies than in actually enjoying your time online. It's a trade-off, and really depends on your level of comfort with cookies. The bottom line is this: cookies really do no harm to your computer or your Web browsing experience. It's only when advertisers are not as ethical as they should be with the data stored in your cookies where things get into a bit of a grey area. Still, your personal and financial information is completely safe, and cookies are not a security risk.
Cookies, small text files containing very small amounts of data, were originally designed to make life easier for Web searchers. Popular sites such as Amazon, Google, and Facebook use them to deliver highly customized, personal Web pages that deliver targeted content to users. Unfortunately, some websites and Internet advertisers have found other uses for cookies. They can and do gather sensitive personal information that might be used to profile users with advertisements that seem almost intrusive with how targeted they are. Cookies do offer quite a few very useful benefits that make Web browsing very convenient. On the other hand, you might be concerned that your privacy has the potential to be violated. However, this isn't something that Web users should necessarily be concerned about. Cookies are absolutely harmless.
Cookies are only as dangerous or invasive as you, the Web page viewer, allow them to be. If you fill out a form with your name, address, and phone number, that information can be stored in an HTTP cookie on your machine. The important part to remember is that a cookie can't know more information than you provide to it. If you don't want a Web site to have your phone number, then don't fill in a form that asks for it. Cookies are often used to gather demographics about a computer user. The company doesn't know who you are or where you live or anything like that, but every time you accept a cookie from them, you tell them a little bit about where your computer has surfed that day. Specifically, the page that you are currently on, and the page that you came from. If you frequent running Web pages and natural food store pages, in theory, companies can use that information to target banner ads to your computer. In practice, however, cookies are more often used to track the habits of thousands of people in aggregate.
Controlling and Deleting Cookies