I know of 2 discharges of an kitchen system that stopped a fire before the fire got "too big" both were manual activations of the system ( guy pulled the red handle) Both knocked the fire down. I cleaned one system and the links were " just fine " according to the fire suppresion company that was resetting the system. they did replace the links but the insurance company did not want to replace the filters eventhough one was rainbow colored from the heat. they said as long as the filter was not warped it was still good. I just said OK, and cleaned the system. It started when the "grease recycle" machine they used to clean the fryer oil shot it all over the back of the fryer that was still at 375 degrees and caught fire when the oil hit the exhaust in the back.
Other discharge was just a look at I got when I went in to see if they were intrested in a new cleaning company, I saw the damage and walked on that one....
You are right about the nozzles, I think they are set up as a doomsday device that is the absolute last chance to save the structure, if the fire is in the plenum can you imagine the damage it has done below and to the back wall filters ect????