I have some real world experience of this causing issues, I managed an Anaconda distribution at a large enterprise and for technical and cultural reasons it made sense to make the base install of Anaconda read-only and users who wanted Python with other packages could use venv or conda to create their own environments.
The problem was that pip --user install is fundamentally at odds with conda environments, and would often break even the base environment. A user would pip install something, pip would default to user install because the base directory is read only, and then all of a sudden their Spyder installation would no longer work.
The solution was fairly easy though, we updated the default pip.ini we distributed with the Anaconda install to include a user=false flag (forget the specific config). And it was my opinion that because we controlled the environment and had specific needs it wasn’t worth bringing up or arguing it should be default. But thought people might be interested in a real world example.