Lot of my Windows 7 testing is done in a virtual installation. I run it under KVM and aim for small disc footprint, I have a number of other boxes there too. One day I came to realize that my Windows 7 installation is running out of disc space. That would be strange, I literally have nothing installed in it and it still manages to eat up 30 GiB of space.
There is Microsoft KB Article ID: 2795190How to address disk space issues that are caused by a large Windows component store (WinSxS) directory explaining this behavior.
The fix is to use Deployment Image Servicing and Management tool DISM. Run something like this as administrator will help:
it will say something like "Removing backup files created during service pack installation". It will remove more than 4 GiB of space. Rest of the garbage will stay on the drive as they originate from regular windows updates.