The diff in a monitored approach vs a normal approach is in the fact that the Capt is PM. This allows the Capt (the pilot with the most experience and responsibility) to monitor. The Capt/PM is also always heads up in final phases of the approach, therefore allowing for an easy assessment of the landing conditions at minima. In my last company, it was used for all Cat II/III and NPA approaches with cloud base and viz below a certain limit. It works well. I know SAA used it for decades, BA also I believe. Who else?