Linus Torvalds [off-list ref] writes:
(This is in no way really fundamental, and the server could cache the
packs it generates for initial clones, but that isn't implemented yet, and
probably won't be for some times).
Performance perceived by cloners is helped by
$ mkdir -p .git/pack-cache
$ git-rev-list --objects --all | git-pack-objects .git/pack-cache/pack
on the server side. This exact example of preparing by the
repository maintainer is optimizing for a wrong case, and I do
not think it is worth doing in practice, but this will give you
the lower bound when server side cache is implemented to do it
on demand.