Pick a random article about a data centre, and see what it is about. Presuming nothing awful has happened at that data centre, it's almost certainly about some way the company has found to save money, and that usually means doing something innovative with cooling. And that is saving a hell of a lot of money. I'd be interested to see a break down of the energy consumption of a data centre; I imagine cooling is the biggest output (though I'm happy to be proved wrong). And it's probably easier to halve cooling output than it is to halve the number of servers running, as improving the efficiency of a data centre seems like a much more isolated task compared to improving the efficiency of potentially thousands of programs written by several hundred teams.