This used to be considered a high level of cheese (In Dom1), because the AI wasn't smart enough to have a threshold of gem usage (as it does now, sometimes to people's displeasure).
While it certainly is something you will find in every game with competant opponents, I don't consider it cheese in any way.
More often than not, if you are going to have certain mages casting certain types of needed spells (Flaming Arrows, Wind Guide, Wrath, etc), it is best to make sure you find a happy medium of gems to be 'wasted' on such tactics.
