This is an unique technique for WinXP. We know that it is necessary to wash registry and TEMP files for Win9X/ME/2000 periodly. Prefetch is a new and very useful technique in Windows XP. However, after using XP some time, the prefetch folder can get full of rarely used or obsolete links which can slow down your computer noticeably. My suggestion is: open C(system drive):/windows/prefetch, delete all files (or at least those more than 3 weeks old), reboot. I recommended that you do this every month.
Editor Note: Deleting prefetch files too often (Every reboot) can decrease system performance!