e.g. if you want to try out helix, you could run `nix run nixpkgs#helix`, and it would download + run helix without installing it. (Or you could run `nix shell nixpkgs#helix` to add helix to the PATH in the current shell, without installing helix, etc.).
One use case I'm excited about for developers is the ability to declare the dependencies needed to build the project. -- So rather than copy-pasting `apt-get install` commands, you'd rely on nix to fetch the installed dependencies. (e.g. I love that I don't have to worry about what packages to install to work on qmk_firmware, or repos which provide a nix shell).
VSCode's Remote Containers supports a similar workflow to the latter.. but, it relies on containers.