When you write information to a disk it can be placed anywhere on the disk. When you scan disk it cleans up the disk and places the info in nice neat blocks that sequence. You create better access time, clean disk and opens up more space. It's like cleaning up your room after you have trashed it by coming home late everyday from doing long hour web projects.
Run from start>Programs> Administrative Tools
We run approx every two days, and every day on our servers
