Yep. Works wonders if you are suffering heavy casualties by enemy archery, flyers or Precision-dependant battle magic. It multiplies the value of infantry and cavalry if you have the upper hand in those
I think also Prec-100 spells are unaffected.
Also don't forget that, like Rain, it reduces the power of Heat (the heat-spreading units I mean) and makes Fire battle magic more fatiguing to cast. *hint-hint*