Hello, the use case is that you can count what you usually don't store (for example different IPs connecting every day to your server), or you can count what is

Hello, the use case is that you can count what you usually don't store (for example different IPs connecting every day to your server), or you can count what is usually stored but it is too expensive to count otherwise (Like iterating a database table and counting unique items in a given column). Also since it is so cheap, you start counting even things that could be unreasonable to count otherwise but that may provide useful insight, for example unique users accessing the site for every hour of the day, unique words ever used by a given user in her comments, and so forth.