I have XP so the SxS folder is only 32MB (23MB compressed). Looking through the folder and searching for descriptions of the DLL files in the folders, it appears that the system root certificates and some runtime libraries like C++ reside here.
It's also possible it may have catalog-security files.
I'd leave it alone until doing further research.
If you must delete folders, I would start out with moving a few to a backup folder for a while just in case something goes wrong.
Compressing this disk folder will also save space. Go ahead and compress the whole disk folder by folder when you have time--it's worthwhile.
I would not even recommend doing anything else without backing up your entire system on an external drive. Then you may experiment.
If anything goes wrong, I wash my hands of it. YOU HAVE BEEN WARNED!
As for me, I'm leaving as it is. I'm monitoring which files get added and altered each day to see what happens.
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