Originally Posted by Great Cornholio

I may be totally wrong, but I was under the impression that the monitor freq was just a carbon copy of what was transmitted on tower freq. Just like when one guy is up in the tower working local and ground all of his transmissions broadcast over both freqs. So when the local controller transmits it goes out over both tower freq and the monitor freq so that if tower freq transmission is blocked by an aircraft the transmission on monitor remains "unblocked" and readable to the aircraft in the area. Its also my understanding that the monitor (who is in the TRACON) also transmits on both the tower and monitor freq for the same reason.