System File Checker is one of the tools used for troubleshooting an OS problem.
When you run sfc /scannow it scans all the OS files and replaces any that are corrupt, so you may not find any afterward.
There are several reports of a windows update that caused a system file checker error, corrected by uninstalling the update.
What kind of problem have you had to prompt the running of sfc, and did you notice any unusual behavior after one of the Tuesdays Windows Update downloads?
I ran it trying to find out why sleep stopped working for me. I have another PC that runs windows 7 pro 64 and sleep works fine. So i figured it had to be an OS issue well sleep seems to work now but still won't auto sleep. So i ran the checker, the computer runs fine never had any issues which is why i was suprised when it found issues i've run the scan atleast 10 or more times since monday. Its still says there are corrupt files. But the log never shows any corruption.
That is a mind bender! SFC says there is a corrupt file, fixes is automatically, nothing shows up in log to specifically check that file separately.
If you updated to Win-7 SP/1, there may have been an OS config setting getting reset. You probably have checked in the Power management section to confirm the settings you want, and the BIOS to make sure it wakes up on whatever you choose (mouse, keyboard, network).