Exhibit 1, the illusionist. Spells like 'rockfall' that hit all enemies on the map, but they do piddling damage for a ridiculous mana cost -- 28 mana, meaning once every 3 turns if he does nothing else.
Exhibit 2, the cannoneer. Another unit that doesn't seem to do much, although he can attack from way the hell across the map. He just can't attack for much. The fusilier gets things like 'stop shot', the cannoneer gets things like 'make your next attack do double damage'.
Exhibit 3, a mission where a bunch of enemies were about 1 level less than all my good characters, and the law was 'no harming the weak'.
So, all my weak units get loaded onto the map to try to fight these higher level enemies without pissing off the judge. I have the cannoneer use 'ether shot' on the illusionist because, hey, at least he can fire off his big spells, even if they probably won't do much. Woah, ether shot restores *60* mana? That actually doesn't suck, he'll be able to cast.
Okay, the illusionist is up. Not my main illusionist, mind you, who's learning half MP -- the backup illusionist who was only learning illusion spells as a sideline because I never expected to use him. Oh crap, I left Turbo MP on him again, so it's 56 mana for each spell.
... and he can cast them, 'cause I just ether shotted him. He can cast them EVERY TURN if I keep ether shotting him. At double power from turbo MP.
Now witness the power of my fully armed and operational battlestation! MUA HA HA HA.