Why should we use venv virtual environment?

[cccat6]

In the instruction, all of the Unix like systems are using venv. Are there any specific reasons to use virtual environment?
I tried to install Chia-1.0.5 directly through pip, and it works fine.
If it does not affect anything, it is not necessary to use venv, right?
I am so confused about it, could anyone explain?
Thank you!