With Windows Vista, the WinSxS folder was able to be cleaned up via a third party tool (WinSxS Lite here – Vista only!). With the initial release of Windows 7, we lost that capability – but it has since returned with Service Pack 1.
The WinSxS folder is used to store install and uninstall files, windows packages (current and previous versions of a component) and out-of-band releases. You should not completely delete this folder. Post Windows 7 SP1, there is now a way to remove the unnecessary files from this folder using the command line (elevated/admin mode -> Click Start -> Type “cmd” in Search. Right click on “cmd” and choose “Run as Administrator”). This is great for reducing the Windows folder size for SSDs and netbooks.
dism /online /cleanup-image /spsuperseded