WSCs are often used in an interactive manner with end users, as mentioned in Section 6.5. This interactive usage often leads to time-of-day fluctuations, with peaks correlating to specific time periods. For example, for Netflix rentals there is a peak during the evening periods of 8–10 p.m.; the entirety of these time-of-day effects is significant. Compare the per-server TCO of a datacenter with a capacity to match the utilization at 4 a.m. compared to 9 p.m.