When you want to service a Windows installation by adding or removing a feature, the package containing the binaries for installing that feature can be in one of three states:
Packages that are not present in the WinSxS folder can still be installed in Windows Server 2012 if you use the –Source parameter for the Install-WindowsFeature cmdlet to specify a mounted .wim file—or you can omit the –Source parameter and allow the package needed to be downloaded from Windows Update. The new Features On Demand capability in Windows Server 2012 also allows administrators to remove packages from the WinSxS folder, something that could not be done on installations of previous versions of Windows.
Carsten Siemens edited Original. Comment: Pirated Content - see my comment
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Content was taken from: "Understanding staged features"
Published by Mitch Tulloch on 21 Nov. 2012
www.windowsnetworking.com/.../Understandingstagedfeatures.html