Except in the case of static or read-only websites, you almost always need to be able to identify your users in a web system. Sometimes the goal is to memorize what the user has already submitted, remember which logged in user they are, or where the user has visited. Sometimes you want to identify which users are real humans and which are automated search engines, or automated spam bots. Whichever your need, there are very straightforward ways to track your web users.