Just a small change that would simplify identification on servers that might have many containers running. It also helps in some monitoring tools that monitor containers.
For example, Beszel’s monitoring system now shows the container names, but it just says app as opposed to docker ps which shows the image name which includes the name discourse.
I don’t know about it the usefulness of this, but I’m quite sure sure the vast majority of self-hosters only have Discourse running on their machine.
Also, such a change would render hundreds and hundreds of posts here obsolete wouldn’t it? 
If you rename your app.yml something else, it’ll use that name.
Also, there’s this setting:
## Uncomment if you want the container to be started with the same
## hostname (-h option) as specified above (default "$hostname-$config")
#DOCKER_USE_HOSTNAME: true