Supervision has many benefits besides automatic restarts after crashes. Supervising programs provide a consistent way to start, monitor, and log long running programs. Nginx reinvents its own interface for some of this functionality (like daemonizing, log rotating/compression, conf reloading, etc.), but it's useful for all services to work under the same interface. This is especially true for monitoring nginx's status, where a supervisor like runit is much nicer than 'pgrep nginx' or 'ps aux | grep $(cat /where/nginx/dumps/its/pid)'.