I agree with the above sentiment. I think AoE without friendly fire loses a lot of tactics. You can just spam those fireballs at point blank range within your entire party. With AoE and FF, you suddenly have to aim your Cone of Cold in such a way to not hit your allies, and communication with your allies as to when to fire a fireball becomes important, etc.
You also get options to balance spells/effects. You might have an AoE that doesn't effect friendlies, and another one that does. You can make the second one be more powerful, do more damage, have less warmup time, etc.