There's a link in the article which explains why
(I do add my virtualenv's `bin/` directory to my path, but mainly so my editor can find the right tools, so I do it from elisp instead of bin/activate in a shell)
I guess I've never looked, does virtualenv provides a bin/pip which already knows the path of the virtualenv? Does the bin/python in there come with a path that uses the project pip install?
I would only use 'bin/python' directly from scripts called from cron, or other similar places.
Best part is you can't accidentally install a package in the wrong venv this way.
I hate modal systems...