As a White Mage, I can say that while Triple regens (Regen + Medica II + Aspected Benefic on Diurnal Sect) can top off a tank in no time, I feel that the run is easier when that AST is on noct, since my regens are powerful enough to keep the party on and noct has that shields that makes my life easier. Specially if he's shielding the tank before a tank buster.

If an AST go noct and uses their shields, it's auto-comm from me.