probably alters the game a lot because if you think of the chess board kings start about here they can only move one square at a time so to get them to safety will require like four or five um steps for them while you have to move everything else out of the way including the rook that stands here so players might elect to just leave their kings where they are but then they can't really open up in the middle as much because that would leave their kings exposed so it is fair to assume that just introducing this one rule might