Here's a use case I pose every time Nix comes up in these discussions.

For $REASONS I want python 3.7.10, and the full scientific stack (numpy, scipy, pandas, numba, matplotlib, ...) at the latest compatible versions along with pytorch. I don't mind waiting for things to compile. How, if at all, can Nix help me get into an environment that meets those constraints? Can it help without requiring me to find and copy hashes of things?