The stun isn't random, the benefit of the stun is. For example, it can convenently interrupt a Furious Roar. Or it can occur between them.
Particularly on 10 man (which is what the majority of the posts prior to the one where that quote is from were discussing) the longer you spend killing adds, the harder the fight is because the fight is harder to handle when there are multiple things to handle with limited people. The amount of effort spent killing Slate Dragon is generally ignored because it you already have to tank swap regardless and why bother killing it if you don't need to in the first place. In 25 man it becomes more trivial since more players can always handle more mobs easier simply because they have more people to assign to the task.
"In anything, if you want to go from just a beginner to a pro, you need a montage." /w TankSpot WTB Montage for Raiders.