I worked on a computer today which needed reformatting because of massive failure from viruses and spyware. They handn't followed the "Castellini on Computers Approach to Security" so the computer needed my help. When I need to perform a reformat, I need to have all the original software or restore CD's to get everything up and running again. If my customer doesn't have the disks, then I have to search the Internet for their particular system.
The most important disks contain the information that tells Windows how to interact with your attached hardware (drivers). Usually, they are contained on either a restore CD or a CD marked Drivers and Utilities. Keep in mind that you can save time and money by putting all the original documentation and any disks that came with your new system (except for the AOL disk) in a manilla envelope or big zip lock bag. This is all important and vital information to your computer.