This should be used with virtualenv, not as an alternative to it. I have a bunch of libraries and tools in almost all of my virtual environments that are not application dependencies and have no business being installed in my production environment (e.g. bpython, tox, flake8, and neovim). This approach also handles things like a dependency being dropped gracefully (if some library no longer needs a dependency, it magically gets removed from your locked requirements.txt next time you compile requirements.in). Python's package management tools are making great strides (see pip's recent peep-style hash checking support), and pip-compile is a big win in that category in my opinion.