[andrewaylett]

You may have not realised that legitimate email has failed (and it might even be true) but my experience suggests it's unlikely that it hasn't happened. I only have a handful of users, but when I was greylisting I'd get reports of missing mail at least annually.

Which isn't to say it's not worth it, although nowadays I'd recommend that https://www.postfix.org/POSTSCREEN_README.html pre-greet checks are just as good at stopping spam and better at not blocking legit mail.