Specifically, for Shadowflare, it's to be up at all times. It's a DPS loss otherwise. It can be used without Swiftcast, but preferably with it. I mean, some good logic for it would be if the enemy was standing withing a certain radius for like, 3 seconds then cast Shadowflare, as more often than not that means it won't be moving again.
Something along those lines. Right now, it waits for Shadowflares "Buff" to run out then recasts it which, in practice, isn't practical for maximum DPS. I mean, it works fine for now but I could suggest a sort of "Opener" followed by a priority list to maintain.
Last point! The option for CDs to be used against bosses isn't working. It stops usage all together and doesn't use them at all, as opposed to against bosses only.