Do I need to use virtualenv with Vagrant?
If you run one vagrant VM per project, then there is no direct reason to use virtualenv.
If other contributors do not use vagrant, but do use virtualenv, then you might want to use it and support it to make their lives easier.
I was used VirtualBox manual setups with virtualenvs inside them to run Django projects on my local machine. Recently I discovered Vagrant and decided to switch to it, because it seems very easy and useful. 
But I can not figure - do I need still use virtualenv Vagrant VM, is it encouraged practice or forbidden?