In a linkshell I used to be in, I suggested a 24-hour ability that would combine the two-hour abilities of your main job and your subjob. So if you were a RDM/BLM, you'd get both Chainspell and Manafont at the same time. Now THAT is useful if you get in a sticky situation. Sometimes by the time you realize you need Chainspell, you might have no convert available and you may be low on MP. And as one who sometimes likes to solo as RDM/PLD, Chainspell-Invincible would be nice. :)