WinSxS folder contains a copy of protected system files and DLLs. Windows Resource Protection mechanism checks the integrity of the protected system files periodically and re-installs any protected file from this folder if its integrity could not be verified due to a compromise or corruption.
After each Windows update, some system files are changed by Microsoft. However, WinSxS folder still keeps the old files along with the new system files in case the updates are roll backed. Therefore, size of this folder keeps growing and growing with each update, especially after each service pack installations.
Finally, you can shrink or reduce the size of the WinSxS folder on Windows 7 SP 1 by using the following command (if you are not planing to uninstall the service packs):
- DISM.exe /Online /Cleanup-Image /SpSuperseded