sudo pip install VS pip install --user
$ sudo pip install Installs the package globally in your python installation, i.e. for all users.
$ pip install --userInstalls to the local user directory, i.e. ~/.local/lib/python -- just you.
Example:
$ sudo pip install jupyter$ jupyter notebookWill run jupyter, open a web browser, allow you to work with notebooks.
$ pip install --user jupyter$ jupyter notebookWill do nothing until your local directory has been added to your PATH.
There was recently malicious code included in pypi. Never use sudo to install with pip. This is the same as running a virus as root. Either add your local folder to your PATH or use a virtualenv.
sudo pip install probably means that you want to install a package system-wide. For some packages, such as virtualenvwrapper, that might be useful, but besides that I'd avoid installing system-wide packages and create a virtualenv for each application and pip install to that virtualenv (which can be done without sudo).