Cooldown usage is typically used by tanks during a time of very, very high damage due to mechanics or just dangerous attacks(see above: Garuda-Suparna Double Wicked Wheel. That thing will hurt.). If there isn't a period of extremely high damage (which I don't think exists), then cooldowns should just be used if you're below half. At least, that's when I'd use it as a tank. I don't tank often though, so take that opinion with a grain of salt.
"Critical fails; for when the GM sobs at night and the players get free checks."
