I use nix today for ci/cd to build a large C++ project for a variety of architectures using cross-compiles. While it could be done with adhoc scripts, some cross compiler tool environment tool + conan, or something else, I effectively wrote my nix expression once to package up everything, and simply changed the target arch and libc and got what I wanted.

It's not perfect, but it works, its fast, and its better than the alternatives.

I'm interested in rying Guix at somepoint instead as I think using Guile might be easier than learning the Nix language, cli tools, and more. I think guix could do much what I do now as well.

I can't see myself using guix as an OS though, since they seem to think systemd is evil or something, and really systemd is quite nice in practice in my experience.