I also put virtualenvs in a single centralized location (~/.virtualenvs), and manage their contents via Poetry.

The main reason is that I sync my Git projects via Tresorit (“encrypted Dropbox”). This lets me switch computers without committing and pushing code that is not “ready”; makes it easier to sync all projects I work on to my backup server; and lets me copy around project files that I don’t want to commit (e.g. messy WIP and TODO notes).

This doesn’t work well with virtualenvs inside a repo, because (i) the virtualenvs are not portable, and (ii) syncing a virtualenv is slow. Instead, I sync a Poetry lock file, which makes it trivial to recreate the “same” virtualenv on other machines.