Does Magic Matter?

In fantasy games, particularly fantasy RPG's, the level and frequency of magic do a lot to define the world.  When you say how common magic is, you say a lot about the world.  One of the real issues isn't how common magic is, it's how common simple magical effects are, and the reality is that, while it matters a lot, so long as the effort to make magic makes sense compared to its frequency, it doesn't really matter at all.