I would have imagined that best practice was for the admin to install commonly used packages in the site library (if that what it is called= /opt/R/3......./lib).
However the local admin regards best practice in terms of performance is for users to install packages in local libraries. I can understand this in terms of keeping the install "clean" and reducing the admin work, but not performance.
I am not saying users should not have the ability to install locally. I just wondered if a new system would be better with commonly used packages already installed on the nodes.