From Business Insider's good, long profile of Larry Page:

In 1999, for instance, the method by which large Web companies such as eBay, Yahoo, and Google added server space had become fairly routine. They purchased servers and installed them in cages at giant warehouses owned by third-party vendors. The warehouse companies would pay for the power that kept the servers running and the air conditioning that kept them cool, and the website owners would pay for space by the square foot. Page figured if Google was going to pay per square foot, he was going to stuff as many servers into that space as he could. He took apart servers and began hunting for ways to shrink them. The first thing to go? All the off switches.
“Why would you ever want to turn a server off?” he reportedly asked.
Stripped of useless components and fitted with corkboard to keep wires from crossing, Google developed new super-slim servers. They looked ugly. But before long, Google would end up paying the same price to host 1,500 servers as early rival Inktomi paid to host 50. As a result, Google’s search ran a lot faster, and Inktomi, along with many of Google’s other search rivals, was left in the dust.