The shield usually doesn't last long enough to do anything, but there have been a few occasions when I've used succor before the fight. Mostly for ifrit if it's not the most organized group, to prevent a wipe when someone pulls aggro by attacking too hard, too soon. Most of the time it's pointless, though. The party shouldn't be taking damage that early in the fight. A preemptive shield on the tank can be handy if you don't have stoneskin, though.