What does “ICACLS C:\Windows\winsxs” do?

That article is pure nonsense. icacls works on object.

The command icacls "C:\demo\example" does nothing else than display the permissions currently set on the folder. For example:

This means that the command ICACLS C:\Windows\winsxs does nothing that needs a reboot.

On another note, the folder C:\Windows\winsxs is an essential Windows folder and should absolutely not be touched as regarding permissions. Changing the permissions on this folder can cause serious problems in the future.

Conclusion: Better ignore that article (or at least that part of it).

No, the command doesn't do anything unless you tell it how to modify the SD. That's something the article forgets to mention.

I have the feeling that it was written based on generic instructions such as "You can use icacls to modify a folder's ACL" – but the article's author didn't understand what they were writing about and assumed that the command would perform all necessary modifications without any further input, which is not the case.