Thank you, NukeCad!
I'm hoping CCleaner will add your sentence, "System and application files often need more than one copy of a file in different places to work properly" to their Duplicates Finder to the end of their 3rd paragraph under "Which Duplicates Should I Delete?" (https://support.piriform.com/hc/en-us/articles/204950144-How-do-I-use-CCleaner-for-Windows-Duplicate-File-Finder-)