A question about disease twisting
Hi all, I am relatively new to the DK DPS -- been at it at 80 less than 2 months -- and I have recently learned about disease twisting.
The idea seems clear enough: change their order of refresh to let one drop, so that each refresh cycle one disease gets in its last tick. However, I don't understand why then we shouldn't let both diseases drop off. The reasoning which justifies letting one drop -- getting the last tick in, despite the lost buffs (in my case, Icy Talons for FF, Rage of Rivendare for BP, I am 0/17/54 Unholy) -- should apply to let both drop off, thus getting the extra tick on both diseases.
So what is the reasoning behind letting one drop, but not both? I am especially curious about the Unholy case, as letting FF/BP drop off with still leave Ebon Plague up, so at least one disease will still be on. Is it the question of rotation -- i.e. I would have an empty GCD if I waited for both to drop? If so, should I then let both drop if I have something to fill that GCD with, e.g. an extra Death Coil from AMS or an extra BS from Rune Tap?
I have searched for an answer, but couldn't find any substantive discussion of the theory behind disease twisting. Most discussions seem to begin and end with "let one disease get in the last tick".