In Hexmapper, they're very quick to make and look quite attractive, which are both big bonuses.
They reinforce creativity when you're doing your wilderness, because each hex encourages you to put something interesting in it. It sort of poses a "what's here?" question. There always seems to be more interesting things and locations on hex maps, perhaps because of this.
Likewise, during the game itself, you can pinpoint the hex the players are in, giving a definite feel of location, rather than a slightly more abstract one that a freeform map with a scale might have.
So...thumbs up to hexmapped wilderness.
On a related note, though, anyone know how many miles wide is your average mountain? Would help in determining how many hexes of mountain terrain to use to signify a single mountain...(yes, I know I may be asking a sort of "how long is a piece of string" question, here).