importance of virtual environment setup for django with python
A virtual environment is a way for you to have multiple versions of
python on your machine without them clashing with each other, each
version can be considered as a development environment and you can
have different versions of python libraries and modules all isolated
from one another

Yes it's very important. For example without a virtualenv, if you're
working on an open source project that uses django 1.5 but locally on
your machine, you installed django 1.9 for other personal projects.
It's almost impossible for you to contribute because you'll get a lot of
errors due to the difference in django versions. If you decide to
downgrade to django 1.5 then you can't work on your personal projects
anymore because they depend on django 1.9.
A virtualenv handles all this for you by enabling you to create seperate
virtual (development) environments that aren't tied to each other and can
be activated and deactivated easily when you're done. You can also have
different versions of python

You're not forced to but you should, it's as easy as:
virtualenv newenv
cd newenv
source bin/activate # The current shell uses the virtual environment
Moreover it's very important for testing, lets say you want to port
a django web app from 1.5 to 1.9, you can easily do that by creating
different virtualenv's and installing different versions of django.
it's impossible to do this without uninstalling one version (except
you want to mess with sys.path which isn't a good idea)
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.