I DPS in dungeons, but only if I know the tank can handle the extra damage and I'm confident the tank can take a couple seconds more of beating without constant heals. Lots of tools and a decent mp pool. No reason not to if you can. Primals and Coil I do not due to the chances of huge damage possibly taking out a DD or Tank. My extra damage will not make that much of a difference compared to keeping the party alive. If damage needs to come from a healer in those instances, then there's a bigger problem that needs to be addressed.