I am looking into using Git for my photos/videos backup external HDDs and the reasoning is simple. It's not about keeping track of changes within the files themselves since like you said, they (almost) never change. Rather, it's about keeping track of changes in _folders_. That is, I want to keep track of when I last copied images from my phones, cameras, etc. to my HDDs, which folders did I touch, if I reorganized existing files into a different folder structure then what are the changes, etc. Also it acts as a rollback mechanism if I ever fat finger and delete something accidentally. I wonder if there's a better tool for this though
Then I think some syncing software like rsync will probably be better. Now sure how often you keep changing archived folders. I split that work TRASH like dirs and archives. When I done w/ files, I move them out of TRASH do proper place and that it. I prefer KISS aproach, but whatever works for you :)
