On top of that, one can use Guix from the comfort of Emacs:
guix install emacs-guix
The Emacs interface includes Magit-style popup menus, lets you install/remove/upgrade/browse packages, roll back, edit package definitions, navigate system services, and more.
I think Ansible is a little bit of an overkill for this purpose, but also, it's fundamentally a non-reproducible system-configuration-management tool, just like Emacs' built-in use-package system.
Straight.el carries over the idea of reproducible builds from the Nix package manager and applies it to the specifics of the Emacs ecosystem.
So the whole point is to get away from the reproducibility issues of Ansible, use-package and the likes.