Originally Posted by
Kisho
Guard usage is honestly determined on a 'per boss' basis. That said, I doubt you meant it this way Alucin but Guard certainly isn't ideally not used at all :P
Guard isn't just for saving yourself from big attacks: it's also very useful for saving healer mana. These days healer mana is a really precious resource, so anything you can do to minimise the amount they spend is really useful.
So yeah, on a per boss basis figure out the best way to use it. Sometimes you'll want to save it for a big attack. Sometimes you'll want to use it on CD. Every time, you'll want to use it as often as possible.