Quote Originally Posted by Hitokirinomad View Post
I believe the confusion is to why you just wouldn't cast it before RS, so that you then don't have to lose any time on a spell not affected by the buff. Your discussion of potency doesn't address this, it just makes the case that in normal situation SF has priority over ruin, which is super true.
Cast SF first, it should still be up by your second fester, after which you are free to cast it again. Or am I missing something?
..Because that delays RS, Contagion, and Aetherflow CDs?

You should never cast it at the start because you have bigger priorities, unless you're casting while the tank is pulling and you know where he/she is going to place the mob. Don't cast it first after the tank has already pulled.