Onboarding was our canary. At 12 people the setup doc was a wiki page someone maintained as a hobby. By 30 it was a graveyard of broken links.

We gave up on documenting the environment and just made it cloneable. Snapshot a working setup, hand it over, done. First-commit time went from ~2 weeks to a day. (fwiw I work on https://cyqle.in partly because of this)