Recently found out in E1M4 a deathmatch start on the ledge with the blue armor in the north-eastern room of the map was removed, because the player can trigger the monster closet in the corner, and then the single use elevator, which will then rise up too far and close off the closet and potentially trap any players inside. This doesn't affect the single-player campaign at all, but I love learning about obscure ways to break these old-school joints