Is pyenv or virtualenv essential for Django?
No, it's not essential to use virtualenv for Django but it's recommended because it isolates the multiple versions of python or libraries you are using for your projects on your system. If you are not using virtualenv then that library will be the part of your python home directory.
For Example:
If you are using version 1 of some library for one project and later on in other projects you have to use or if it's the requirement to use version 2 of that library then using specific virtualenv (if you are working on multiple projects simultaneously) for that project enables you to use multiple libraries without any problem.
For the first time, I made an environment for Django with virtualbox and vagrant (CentOS 7).  
But every tutorial I saw says I need to use pyenv or virtualenv. I think they are used to make a virtual environment for Django. But I don't know why I need to use pyenv or virtualenv. (For example, Cakephp3 doesn't need packages like pyenv or virtualenv.)  
And I was using virtualbox and vagrant, which are already virtual environment, so I think I was making virtual environment inside another virtual environment. I am not sure if this is meaningful. Maybe pyenv and virtualenv are not necessary if I am using virtual environment like virtualbox or vmware?
Are they essential for Django? When I deploy Django in actual server, do I still need to use pyenv or virtualenv?