If you have a game, where you have large packs of files (like a 2GB sized textures.pak), and in a patch you want to add 2 small things, you can just ship the differencd between the old anc new pack file, and skip transferring the rest.
The game industry really hasn't used binary diffs and patching since the 90s when they used RTPatch.
Flight Simulator downloads tens of GB every time I start it. :-/