Well, on Titan there is still one thing you can do if you run out of mana...



Seriously, though. Titan was (and still is really) scary. I found Ruda and the 2.xx HM trials less stressful.

Based on this I think it is an objectively good thing for tanks to heal and healers to tank, just to get an appreciation and understanding of how we can bast support the other role. Specifically I am learning a lot about what the CDs do so I know when tanks need more heals, or when they're less squishy. For example, convalescence. If I see that icon now I cast ALL the heals until it's over.