[Cainehill]

Not to mention that one-way connections can add a lot strategically to a game / map. Think of a map representing heaven, hell, and earth. Units / armies could go from earth to heaven, or to hell, but not back.

And games like Age of Wonders did, well, wonders with one-way portals, teleporters, and gates, some of which could be destroyed, others (iirc) couldn't.