importance of virtual environment setup for django with python
In most simple way, a virtual environment provides you a development environment independent of the host operating system. You can install and use necessary software in the /bin folder of the virtualenv, instead of using the software installed in the host machine. 
Python development generally depends of various libraries and dependencies. For eg. if you install latest version of pip using sudo pip install django, the django software of the specific version will be available system wide. Now, if you you need to use django of another version for a project, you can simply create a virtaulenv, install that version of django in it, and use, without bothering the django version installed in os.
Yes, it is strongly recommended to setup separate virtualenv for each project. Once you are used to it, it will seem fairly trivial and highly useful for development, removing  a lot of future headaches.
I am very much new to the process of development of a web-application with django, and i came across this setting up and using virtual environment for python.
So i landed with some basic questions.

What does this virtual environment exactly mean.
Does that has any sort of importance in the development of web-application using django and python modules.
do i have to worry about setting up of virtual environment each time
in the development process.