I wasn't able to observe a meaningful performance improvement from it, and it requires some file I/O. Here are the times, in seconds, I observed on my ThinkPad T450s with Python 3.6 and Ubuntu 18.04:
test 1 test 2
master 8.96 2.59
this change 8.88 2.62
Test 1 is the total time from:
$ time dash -c 'git clean -dfx && pip install -e . && pytest --ignore tests/test_bin.py'
Test 2 is pytest's reported total time from a subsequent:
$ pytest --ignore tests/test_bin.py