"The complexity of the formula is what ultimately determines the difficulty of casting the spell, that and how much raw energy must be channeled in the casting. So, instead of trying to cast a spell with a four-times potential but a sixteen-times complexity, and probably failing and getting hurt in the process, we cast the normal-potential spell but use a ritual to amplify and expand those parts of the formula left open for elaboration. The casting takes significantly longer, but the complexity is minimized, the potential increased significantly, and the danger limited."