It's useful when developing. Not being able to shell into the production system is fine if you can shell into a staging/development system. If you are running

It's useful when developing. Not being able to shell into the production system is fine if you can shell into a staging/development system. If you are running Docker containers and you can shell into local containers, that is usually "close enough" that you can do useful troubleshooting. But fly.io (and CloudFlare workers, etc) are different enough from off-the-shelf containers that it is very important to be able to poke at containers when they break, even if they are not the actual production containers.