Ever a reason to not use Darkside?

I was just in a party with a DRK that did something I'd never seen before. They kept Grit up full-time, which is normal for Duty Finder content, but during AOE pulls, they turned off Darkside (they definitely didn't just forget, because they kept specifically turning it on or off at various times). I don't play DRK that much, so I'm used to just leaving it on 24/7.

Is there ever a reason to not have Darkside on (aside from between-combat to regen MP if you really want to), or was this guy just weird? I couldn't come up with any particularly good reasons why they'd be turning it off. They could regen MP, I guess, but in combat, that doesn't happen very quickly.

Honestly? No. Turning off Darkside cuts off a ton of your abilities, and the MP regen during combat doesn't outweigh the cost of re-entering Darkside. MP still regenerates outside of combat, regardless of whether or not Darkside is on. The only situation where it might be worth it is during very long phase transitions in later raids, where the MP regen might outweigh the cost of Darkside. And, of course, it's also a major DPS loss. Otherwise, it really should be up at all times.

the only reason to turn off darkside is when bosses have long downtimes where you can spend the time doing nothing to recover some MP but apart of that no, you should never turn it of if you are fighting.

Cool, that's what I thought, thanks!