Less of a pain in the ass for rapid iteration, zero overhead, fewer dependencies = less complexity. Virtualenv is literally a set of shims in your $PATH and so

Less of a pain in the ass for rapid iteration, zero overhead, fewer dependencies = less complexity. Virtualenv is literally a set of shims in your $PATH and some tooling to manage those sets. Pyenv is the same thing, but extends the concept out to your actual Python interpreter and lets you rapidly switch between them.