75% is the magic number
When you add up all of a combat rogue's damage sources, you find that Deadly Poison and Rupture don't contribute much. Your average combat rogue is dealing about 75% of his damage via attacks that are valid for replicating through Blade Flurry. So, when we activate Blade Flurry and there are two targets nearby, you can expect those sources to grow to deal 105% of our original damage, right? Negative, the math isn't quite that simple.
Sinister Strikes are replayed through Blade Flurry, but by activating Blade Flurry itself, you cut your energy regeneration, which means you can't use Sinister Strike as often. The energy cut has to be factored into any math involving Blade Flurry. You'll be dealing 40% extra damage with each Sinister Strike, but you'll be unleashing 20% fewer of them. You'll also be using fewer Eviscerates and fewer Revealing Strikes along the way as well.
For pure cleave, the energy loss is moot
Turning on Blade Flurry when there's two targets nearby will immediately boost your overall DPS by about 20%. There's no situation where you won't want to activate Blade Flurry when you can cleave your damage to a second target. While 20% isn't exactly the 50-60% boost we used to see when cleaving, it's still obviously worth using.
Blade Flurry only scales up from there. Because we only take the energy penalty once, the damage bonus goes up dramatically as we add targets. We'll be dealing 50% more damage against 3 targets, 75-80% against 4 targets, and over 100% extra damage to 5 targets. The ability to double our damage when facing large groups will definitely help combat become a powerful cleave spec. Considering that many dungeons and challenge modes are designed around this type of small-scale AoE, combat is looking very good in patch 5.2 and beyond.
What about boss fights?
Unfortunately for us, two-target boss fights are extremely common compared to five-target boss fights. In fact, the only multi-target fight in this tier is Wind Lord Mel'jarak and his minions. Meanwhile, we've already seen a handful of two-target cleave encounters like the Stone Guard, Garalon, and Amber-Shaper Un'sok. A 20% boost is still a nice perk when facing Garalon, but it's nowhere near the level of cleave that we were previously able to obtain.
Our two-target cleave capabilities are being nerfed, there's no doubt about that. However, combat's ability to handle more than two targets is being dramatically amplified, which makes Blade Flurry our best friend against trash and in dungeons. Because Blade Flurry only scales to five targets, assassination will continue to dominate large-scale AoE situations with its Deadly Poison and Envenom combo.
Fan of Knives factored in
If I didn't know better, I would probably assume the Fan of Knives and Blade Flurry would have some interesting interactions. Blade Flurry cuts the number of FoKs we can use by reducing our energy gains, but Fan of Knives scales well as the number of targets increases. Is there a break point where the number of targets is so great that we would actually turn off Blade Flurry to increase our FoK damage?
The answer is no. Fan of Knives is pretty bad for combat rogues. When we looked at assassination's AoE damage, we saw that Fan of Knives was contributing less than 5% of its overall damage. Fan of Knives is even worse for combat rogues, as we don't see the massive contribution that assassination's poison damage adds to FoK. In fact, the top-ranking combat rogues facing Wind Lord Mel'jarak aren't even using Fan of Knives at all. When faced with the ideal encounter for Fan of Knives, it still fails to be worth casting.
All Blade Flurry, all the time
There is no reasonable point at which you'll want to switch from Blade Flurry to Fan of Knives. Unless you're so inundated with targets (around 15) that Blade Flurry is simply a drop in the bucket, just keep it active and keep doing what you're doing. I don't anticipate facing that many targets at once, and definitely not in a raid environment. If you're going back to fight Onyxia and someone pulls a lot of whelps, you might have a case.
If there is more than one target around, activate Blade Flurry. No exceptions. Never use Fan of Knives, but rather focus on dealing good single-target damage so that your Blade Flurry damage is amplified. Crimson Tempest is similarly impotent, since an Eviscerate replayed to five targets is much stronger than a Crimson Tempest. Combat rogues should really just stay away from both FoK and CT in general. Blade Flurry is all the AoE that we'll need for now. Doubling our damage when facing a small group of enemies is quite powerful, and I can't wait to start cleaving through dungeons.
Sneak in every Wednesday for our Mogu'shan Vaults guide, a deep-dive into the world of rogue rotations -- and of course, all the basics in our guide to a raid-ready rogue.