You can choose whether or not to take advantage of it. And of course, you can change the settings or erase the account at any time. In the original design for the Web, there was no way for a Web site to know whether one page request was connected to another. For most sites, this is fine. In a news site, for example, each article is independent of the others.
Visitors see what they want, then leave.
But for those of us selling on the Internet, this is a real problem. We want people to be able to select several products before purchasing them. We want the selection process and the checkout process to span more than one page. In other words, we need a way of keeping track of Web site sessions rather than merely page requests. If you have a personal shopping account, the session ID allows us to remember who you are once you have identified yourself.