I've noticed a lot of people pick a secondary school so they can use the damage spells from it.
I'm not saying it doesn't work, but as you get to a higher level and you get more and more power pips, it becomes less effective and using the damage spells from your own school ends up being better.
It seems like it makes more sense to put points in a secondary school for specific spells, like Reshuffle, Feint, Tower Shield and Satyr.
When you stare into the abyss, it stares back into you. Look that you do not become the monster you hunt.