If you stay in the bleeding edge some setups might break. E.g. package A doesn't work with library B anymore unless you switch back to another version. I have

If you stay in the bleeding edge some setups might break. E.g. package A doesn't work with library B anymore unless you switch back to another version. I have very rarely experienced this problem, and in 8 years time I have never had to roll back any critical packages like the kernel, firefox, emacs or any system utilities. It's not something that bothers me because it's so rare, and I understand it's the product of very complicated setups and bleeding edge configurations. Nix is mostly valuable for simple declarative configurations, the ability to alter package build recipes quickly, and for package and setup reproducibility.