Until you have to deploy on a machine without internet access, and suddenly pip -r requirements is not enough, especially if you don't have a local pip mirror.
I develop a project that gets deployed to some users with locked down boxes (tight permissions, no internet), and it's really not that bad. You just download the dependencies using `pip download package_name` and bundle them with your project. Your install is basically the same; `pip install -r requirements.txt --no-index --find-links /path/localdeps/`.
It's not as nice as just doing a regular pip -r, but it works and isn't that much effort.
