Comments in config are useful in the same way that comments in code are useful --- to point out things that are non-obvious to other people who work on the same config.
Things like listen on port 8081 instead of port 80, because the loadbalancer does something weird. Or this strange config is important because of feature X and blah. Or if you change this here, be sure to change it there.
Things like listen on port 8081 instead of port 80, because the loadbalancer does something weird. Or this strange config is important because of feature X and blah. Or if you change this here, be sure to change it there.