Can't remember many specific bosses for sure, but there's been a few times. One was during a 1 tanking (Pally if I remember correctly) madness LFR fight (cat druid qued tank, started the fight then left). Tank died once near the start, I used my Brez, once on the third platform (only other brezzer used his), then he died a third time just as the final phase started. People started dropping from adds. It was a tense 15 seconds, but thankfully the CD on my brez finished up so I was able to get the tank up (though I died in the process) and he went and picked up the adds just in time.