Over 10 years ago, it cost a lot to keep computing facilities running, with masses amounts of money being required to keep a CPU going for only a few hundred cycles. For this reason, it was important to keep track of who was using the CPU, and how much they were using it.

Universities and companies used to keep track of this information, and then bill their students or customers accordingly.

Although it costs far less to use CPU time now on most standard PC systems, you may still sometimes want to have this functionality; perhaps if you have a large rendering cluster than you're renting out to CG companies.