I never understood prepping. Either you have your character's abilities to require prepping as a means of bogging down their power level, or you simply don't prep and attack right off the bat.

Example: a character capable of launching a gigantic icebergs at his foe faces off a pyromancer powerful enough to only launch a tiny fireballs. What can you do to even them out? Have the ice mage prep for his iceberg attack.

As i see it, prepping is something applicable only to those abilities, which are meant to be prepped.