They want petabytes. Whether it's on one machine or spread over a couple of machines, they want it all easily accessible for satellite images, intelligence and economics data. There are huge amounts of online help, images, templates for documents, tons of clip art and photos. It burns up space real fast. What you hope is that the disks get bigger so that you don't have to do the housekeeping.
People do something now that was insane a few years ago, which is to keep every e-mail message.
They never know when they might need them. If disk space gets cheaper and cheaper, it changes the trade-offs you make. Your time is worth more than buying another disk. People now expect near-instant access to data all over the world because of the Internet. Caught in the middle are the bandwidths of the computers and the networks.