Comment by bsysop

This is huge. There are a ton of mis-configured Apache and nginx reverse proxies out there that expose the primary domain name of the site being served. You can quickly test this for yourself by running "curl -vk https://your.ip.address" and see what pops up for the CN field or Location header.

Even worse is the pattern of requesting LetsEncrypt certificates for multiple domains on one certificate. Now all of a sudden you're leaking development server hostnames, peeling off the white label of multi-tenant, and making things easier for automated scanners.

I get it that security by hostname obscurity is a poor practice on its own, but there's also something to be said for cutting down a large amount of malicious traffic with some common best practices.