Not the GP, but: For Guix in general? That's easy to answer:

(1) Making things reproducible. That is one of the main reasons. And not only installed system packages. You can also use it to build reproducible projects you develop, if the dependencies are available on Guix.

(2) The other one is installing software, that your distribution doesn't have in standard repos.

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giancarlostoro a day ago | parent [-]

So its similar to Nix? I've heard similar of Nix.

	▲	mikepurvis a day ago \| parent [-]
		Nix and guix ("geeks") are close cousins, and both can be an entire OS or be used just to manage a single workspace/project on another OS. There was a solid piece on here a few weeks ago comparing the two, written by someone with in-depth knowledge of Nix: https://news.ycombinator.com/item?id=44569032