There is a thing called an "action point" as a concept in programming, a place where you have a decision or choice or alternative or SOMETHING where human input is involved in some way. Not even counting the sprites / non-player characters of any modern game, you have an action point at every texture swap on the road because of "handing off" the player from one location to another. If you stop to consider all the edge intersections for all graphic textures in an open-world game (I'm thinking Elder Scrolls III, IV, and V or Fallout 3, New Vegas, and 4, or any member of the Witcher series), the real surprise is that people don't "fall through the cracks" (literally) every time they take a step in-game. What's that old chant that elementary school kids used to sing? "Step on a crack, step on a crack, break your mother's back."
THAT is my idea of a play-tester's nightmare - finding all the edges in an open world.