The only time you should ever turn off darkside is if you're in a fight such as Ravana EX where there's lots of downtime. Usually in my runs there's a bard playing ballad and when he's charging allover the map I turn it off gain mana back or when he uses Bloody Fuller then i'll slap it back on. Downtime is the only justifiable answer to turn off Darkside because there's nothing to tank or swing at.