All of the above is an automatic journald feature. If it logs to syslog, or it's a systemd unit that logs to stderr, journald will automatically add various fie

All of the above is an automatic journald feature. If it logs to syslog, or it's a systemd unit that logs to stderr, journald will automatically add various fields like the PID, and log timestamps with microsecond precision. Logging natively with journald allows you to add custom fields on top.