I have always been using virtualenv for testing my app in localhost since I have isolated environment and can safely test new release of packages.
Now It comes the time when I have to deploy my app to a production server. I am wondering if I should also use virtualenv for production server or just normal installation should do. Since it's production server I can always use the correct version that I tested in the dev server (under virtual-env)
I would do it that way if you ever think you'll run more than one project on the webserver. As soon as you have two projects you run the risk of a future upgrade of any python package breaking the other site.