I first got a lesson on how to read healing meters while raiding Serpentshrine Cavern. One of our healers, an otherwise very competent holy priest, consistently ran OOM early on Morogrim Tidewalker and was next to useless during the final phase of the fight. The head of the heal team took an hour to look over the logs, and decided to give me a lesson on how to read them while doing so. It quickly became apparent that the priest was unwittingly covering for a resto shaman, who not only wasn't pulling his weight, but also seemed to take an unusual amount of damage.
"Why aren't you doing anything during the add phases?" asked the head, a paladin.
"Because our off-tank can't hold aggro for s$#t and I'm tired of dying to murlocs."
This was actually true. Our head healer pondered for a moment. "Can't you just Chain Heal after he's already gotten all the murlocs?"
"No, I die that way too. And we have to save BoP for the clothies who have to AOE the murlocs." Also true.