It could be the diffefence between enlightenment and intent. The spell "intends" to do something, and takes the path of least resistance in order to bring about a result. Understanding the actual machinations of the spell could be an area of idle study for most, since they work anyways without delving too deep. That said, I imagine knowledge of the path a spell takes allows one to change the intent to be that much more specific, theoretically (and situationally) increasing the potency of the spell. It's the difference between casting Fireball and casting Delayed Quickened Empowered Fireball.

Just speculation.