[Serak Moonblade]

well apart from buffing, i find fireball the most useful spell in the game.
other area effect spells can put an entire army out of action - temporarily or permanently! after learning this you must learn ti time your spells and also to place them accurately. a well placed fireball can bring a swarm of goblins to 'nearly dead' and disrupt all the enemy spells exactly as your charging fighters reach the fringe of the area of effect to sweep up the remains.

another indirect gain is that you don't rely on your potions. instead you can sell most of them.

by the time i finished IWD 1, each of my characters had individual potion bags overflowing with potions.

all this takes a wee bit of practice but its not for no reason that it is said that spell casters must be your first targets in a battle.