It's alright... everything is useful, except perhaps summoning a phoenix and using Pacifism, but the axe is really effective...

Pacifism makes sense to cast, especially after leveling it up, as it allows you to maintain the health/damage balance and keep expensive creatures like cavalry or unicorns alive while still allowing them to deal significant, not too reduced, damage.
The phoenix can effectively deal damage in the early days of the game, but that's if you're lucky enough to find it early. However, you can also use the phoenix to:
1) remove retaliation,
2) weaken the opponent by setting them on fire,
3) fight necromancers - by occupying stacks with destroyed undead.
And in Chaos magic, invisibility is very useful in battles against superior enemy forces. A hidden reserve of fairies is a strong trump card. I won the battle against Karador in this way (knight level 24, difficulty - impossible, version - 1.6.4).