I raid with another affliction warlock. We both parse very well, usually in the 80s for most fights, although we both follow our own strat and talents per fight. I was browsing his logs and noticed that instead of letting Drain Soul run it's full cast after stacking UA, he is recasting it three times in a row, probably after each initial tick. I've always understood that that there is no benefit to this.
Is there a reason to recast Drain Soul over and over instead of letting it finish the cast? Does this give better chance of procs or dps, or is this just a bad habit?