The closure size reduction is substantial:

--8<---------------cut here---------------start------------->8---
$ ./pre-inst-env guix size graphviz | tail -1
total: 183.6 MiB
$ guix size graphviz | tail -1
total: 242.3 MiB
--8<---------------cut here---------------end--------------->8---

But I suspect we’d still need the full-blown variant for things like
xdot.

Ludo’.