Based on the article I'd say the main reason to use it is so that you can have what amounts to local packages instead of having to rely on global packages (be they system-wide or user-specific). This is what npm does by default - packages are installed locally to node_modules.
And for replicating production setups I'd rather take it a step further and use something like Vagrant instead of replicating just one part of the setup (Python).
Based on the article I'd say the main reason to use it is so that you can have what amounts to local packages instead of having to rely on global packages (be they system-wide or user-specific). This is what npm does by default - packages are installed locally to node_modules.
And for replicating production setups I'd rather take it a step further and use something like Vagrant instead of replicating just one part of the setup (Python).