Well, here's a fun fact for Windows 7: Microsoft at one point decided that they would allow people to roll forward and roll back updates at-will, and even move to an update at a point-in-time in its entirety if necessary.
Obviously, this is rather insane and takes up a gigantic amount of disk space, and wasn't something they ever implemented. They must have realised this, so they built a facility into their DISM.exe utility to remove all updates that were superseded by the service pack (the switch is /spsuperceded). DISM.exe was released in Windows 7 SP1.
Note that there has never been, and never will be, a Windows 7 SP2, because Microsoft decided to go with the rolling update schedule. What this means, however, is that /spsuperceded will never work as they have never actually gotten to a second service pack.
It appears to me that Microsoft must have forgotten the original plan for clearing out old and useless patch files from SxS, because they rather surreptitiously introduced a new option into the disk cleanup wizard to remove old Windows Updates (to get to it, you need to elevate to admin via UAC in the GUI). This removes the old updates.
I have literally had systems with around 6-8GB of old Windows Update files. The biggest issue is that you think they are deleted, but it appears that Microsoft actually removes the updates after you reboot. I've had one system that took an hour to reboot as it was removing so much junk. I had a friend who had an even worse system, and he had to leave it overnight...
Here's another fun fact (not sure if it's fixed in Windows 10...) but the WinSxS folder is where system files are kept. NTFS does a symbolic link to these folders back to the System32 folder. The problem is that the metadata is updated in one location only, and so if you check the WinSxS folder and the System32 folder, you'll see different file sizes for each folder.