I just happened to stumble across this whilst reading up on the current raspOS position on Python2/3, pip2/3 before embarking on another Python project. It relates directly to my comments earlier in another thread (Problem installing the python-kasa package for use with TP-Link HS110 - #7 by pb66)
So the RPF are recommending the use of sudo with pip(3) and I guess that is for the reasons I give in the other thread, to install the packages system-wide, in the same way the distro package manager does.