I think you mean Darkside. And yea, for now, the de facto rule is to maintain Darkside at all times.
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@everyone
For the MT role though, I can see 1 possibility where this could change:
From my testing, dropping Darkside for the 3 ticks of MP regen is enough to compensate for the cost of Darkside's degen & re-activation cost, and by doing so you're actually placing yourself a little bit ahead in regard to MP degeneration than the alternative of having just left Darkside on.
Coincidentally enough, the time it takes to do a Power Slash combo allows close to 3 server ticks.
I haven't tested much yet, but theorycrafting wise - if Power Slash is part of your rotation - dropping Darkside for it's 3 GCDs, and re-activating it before the next Hard Slash or Syphon Slash (depending on where your DS disabling lands between server ticks) - of the following combo may, over time, result in a DPS increase.
This is because, over time, the DRK toggling DS would have the resources for more Dark Passenger & Dark Arts that a DRK with the identical rotation (but no DS toggling) would not.
Dark Arts potency: (+100 (or +150/250 if no DP at all), +240, +350) is higher than Power Slash combo's +80 potency when left in Darkside. Blood Price is the wild card (if MP isn't needed to max oGCD use and Dark Arts buffs, toggling would serve no purpose, and be a straight -80 potency per PS combo).
Again haven't tested this yet, but if Power Slash is part of your rotation, eventually the MP-conservation of dropping DS for that combo would open up better potency increases through the oGCDs & DAs. Also consider: since Spinning Slash has no MP recovery, our Power Slash combo technically cost MP whilst DS is up - even without the Dark Arts buff for PS. The DS degen is ticking 2-4 times whilst performing a PS combo, but unlike Delirium/Souleater, there's no Syphon to counter-act that degen.
Of course straight Syphon combos and 100% Darkside uptime is absolutely better. And even with good DPS groups, as MT it's rare to have situations where a Power Slash combo is even necessary or at all that frequent.
So it's a long shot that such a rotation method is viable - let alone better.
Could use some testing,