This is a day-to-day use case:
Assume there are many Opportunities on an Org. Now Sales-Reps are uploading some auxiliary information as Files in Lightning using the standard related list and there the Files section (under the hood: ContentDocument and ContentDocumentLink are created). Usually this is large stuff, like Images, Hi-Res PDFs or even Videos...
The tend to re-use these auxiliary files on many Opportunities (since they are selling the same products or services over and over again).
Now using the standard UI, identical files will be redundantly uploaded that means the ContentDocument will be created n-times with the same physical file consuming n-times the server storage. That means on each upload a new ContentDocument will be created.
What I would have expected is, that if an MD5-Hash of two files is equal, Salesforce should re-use the existing ContentDocument and just create a new ContentDocumentLink. It looks to me, that the ContentDocumentLink is just there to make multiple usages of the same file possible. But the standard UI is not using it - at least not by default.
Is there a way to upload files without these redundancies?