Other than for Pull Requests, I've yet to see how GitHub is useful for Perl as people install them from CPAN. Given the number of Monks who use it and have advised me to do the same, I total accept it's the right way to go but I don't totally understand why yet.

It's exceptionally useful. It allows us to fork and clone your project and review/modify/test it locally, in our own environments. It's far less time consuming then downloading a tarball, extracting it, playing with it, then creating patches to send you for possible inclusion. You seem to be in the mindset that devs just want to install your software. We don't. Often we don't want to install it at all, just want to look at it.

Also, as pryrt mentioned above, you get Github Actions to perform automated CI testing on every push to the repo. This is infinitely handy. (A couple of years ago I switched all of my projects to Github Actions from Travis CI). It also allows you to easily revert changes, find when specific changes were made (and by who), run multiple concurrent branches simultaneously then merge the changes from those branches into your main branch once they're tested and stable etc. The version control system is far more useful to yourself than it is outside users of your software, but it is very useful to them too, regardless of the language in use.

Your workflow should begin with the Version Control System, not be an afterthought. Once you've gotten into this workflow process, you'll begin to clearly see how and why it is so important.

Update: Here's one of my basic Github Actions configuration files. It's a file called .github/workflows/github_ci_default.yml in the root of one of my repositories. Do some reading on Github Actions. It'll be worth your time.