What to do while scanning?

I ‘ve always been told that while your computer is scanning something you should have nothing running until that scan is complete. It be your system defrag, virus scan, or some other program.

I ask because when doing my routine MSE scans I’ve noticed a significant difference in the time it takes. Being on the net verses not cuts the scan times in half. Is it passing over those files its meant to scan because the files are being used?

 

I always run it late in the night, and just leave my machine up. At work, I run it during lunch, so that it can do its thing. With Windows 7 & Vista, MS actually made it, were it will run while the machine is idle.