Not empty space, space reduction....

The empty space is usually a saving, it gets utilised for something else rather than sitting idle, which saves the company even more money as they don't need to build more datacenters (which means the World also stays greener). In London I hear floor prices of £50 to £150 per square foot for office space (I'm not an estate agent so don't email me if those prices are low!), that's before you add the cost of converting it into a datacenter room.

Then you have the green savings on associated admin costs - virtualised resources are also usually centrally managed via software, reducing the number of car journeys out at 3am to reboot servers that some numptie has crashed, because now you can sit at home in your pyjamas and do it with a few mouse-clicks (that's if you haven't automated the whole thing anyway). BOFHs reaching for your cattleprods, the secret is out, you will lose a lot of that cushy quad-time call-out money!