Is there any danger of e.g., causing conflicts usi

Question

I am having trouble finding good documentation for pip's --ignore-installed flag. pip install --help says simply:

Ignore the installed packages (reinstalling instead).

Other than the side effect of there being more cruft on your system, since installed packages will not be uninstalled when e.g., upgrading, are there any other known side effects? Is it possible for conflicts to arise with both packages installed? Will the newer package always "win", or is there a danger of accidentally using the old package without knowing it?

I have a situation that calls for me to potentially use this flag, ignoring a number of previously installed packages (because pip version 10 no longer uninstalls packages installed by distutils, but I want to make sure I am not potentially shooting myself in the foot. Thank you!