It plays well with the Debian reproducible builds stuff to weed out as much non-essential variation as possible.

For certain packages, I'm guessing the byte-savings could be near-infinite. Already programs are encouraged to ship `foo` (potentially arch dependent) and `foo-data`, but imagine updating "just one font" in a blob of fonts, and not having to re-download _all_ other fonts in the package.

For some interpreted-language packages, these deltas would be nearly as efficient as `git` diffs. `M-somefile.js`, A-new file.js` and just modify the build timestamps on the rest...

The answer to your question should be relatively straightforward: just run it on a base/default major version upgrade and see how many MB of files have the same `md5` between releases?

It could have really nice observability properties if the delta is transparent and you can see what is flowing by. In this regard, the space savings would be a nice side effect.