> Homebrew packages conflicting with local packages, something you compile give needs a different python/ruby/node/rust/whatever version that you have locally installed, you want to quickly try out a new package or upgrade without changing your system but have the option of rolling back safely, need to quickly install a database, want to try out a new shell and shell config but don't brick your system and have the option to roll back, etc.

Couldn't pretty much all of that be addressed using containers? Keeping your base system clean does sound wonderful, but eg distrobox containers sound more approachable - you're using all the same commands that you normally would, apps are in an environment much closer to what they probably expect. You can still roll back using snapshots, which you can configure to be automatically created on system updates. If you want an atomic rollback guarantee, and a strong reminder not to mess with the base system, you can use an immutable distro (talking about Linux, not macOS here). The one big advantage that I see from nix is reproducibility. But it's not clear how desirable that is for a desktop use case. You may actually want different software on different machines. Having an overview of all the changes you made to your system sounds cool, but I'm not sure it's worth the effort that comes with nix. I'm worried that after 8 months I'll decide it's too much hassle, like many commenters seem to do, and end up switching to a simpler system with dotfiles and containers, wishing I'd done that from the start.