Hotlinking from external sites to Commons images is discouraged, but allowed (https://commons.wikimedia.org/wiki/Commons:REUSE#Hotlinking). Moving a file whilst creating a redirect unnecessarily breaks such hotlinks, because the upload.wikimedia.org URLs don't follow the redirect.
- Uploaded https://commons.wikimedia.org/wiki/File:Example-2.jpg
- Got the hotlink: https://upload.wikimedia.org/wikipedia/commons/8/8d/Example-2.jpg
- Moved the file, with redirect, to https://commons.wikimedia.org/wiki/File:Example-of-move.jpg
- Hotlink now gives a 404 page (and not even a particularly helpful one).
I've deleted this test, but the 404 page is exactly the same as for a deleted image.