The more a server is used, the more efficient it becomes at converting electricity to useful computing operations. For example, a server running at about 10 percent utilization might already be consuming 50 watts. Whereas the same server running at 90 percent utilization might only consume another 50 watts. There are various reasons for this, but one of them is static power draw. The fifth principle of sustainable software engineering is energy proportionality which includes running servers at a high rate of utilization.