You probably want to lay the flooring the same direction in all rooms and lay it continuously through the doorways. The reason is that it looks more real when it looks as if the floor was built before the walls, as it would have been if it were original. You'd only want a transition in a doorway if you're moving to a different type of material. As long as you're laying the same color and type, then lay it all the same direction and continuously through the doors, imo.
I question the statement in bold. Clarify please.