I needed a version of Racket with the latest version of openssl because I needed some cryptographic primitives in the newer openssl that isn't in the default one.
"Aw man", I said, "it's in core-updates (the development branch) and looks already prebuilt there, but I don't want to switch my *whole system* to core-updates."
It turns out with Channels and Inferiors, I don't have to! I can switch over just the packages I need! https://guix.gnu.org/manual/en/html_node/Inferiors.html
Guix is amazing.