I don't play strategy games, but I think it's great in games like BG, it's easy to tell what parts you have/have not explored, so it makes backtracking easier.

Hog of War

always Fog of war, otherwise researching the radar on command and conquer (or was it starcraft, or both) will be useless

Fog of war.

In a strategy game, imperfect knowledge of the enemy on a map keeps a nice level of tension and immersion. I think of it as a commander's viewpoint while a game with the entire map and enemy movements revealed is more of a god's-eye view. The god's-eye view is certainly appropriate in some games, but not nearly as many as the commander's view.