You really shouldn’t, though. If you use a dependency manager for some deps you should use it for all deps. Using a global/system cache would be great if dependencies were versioned and each script could specify which version is needed, but they’re not to my knowledge. And it’s all fun and games until some random install script somewhere updates a global dep and your stuff breaks and you don’t know where to even begin looking.

I’m still waiting for Nix to mature and for its UX to improve.

In my personal experience, it's absolutely necessary. Breaking changes are all over the place. I have non-dev coworkers who have built Python tools without any knowledge of package management, and it's a minefield getting it up and running.

For individualised shell usage, sure. I have global installations of common data science utilities like pandas and jupyter, or requests.

Reproducibility isn't just about deployment, it's also about coordination with colleagues.