Well, for two twilight it might be a really good idea to play. If they draw the cards and you don't move again, then you may have forced them to discard a few important cards.
-wtk
Sure, it's possible you may have forced them to discard important cards, but I feel you're even more likely to have made them draw cards they needed that they otherwise wouldn't have gotten for a turn. And really, if you have 14 cards in hand, after you get done playing a few in your Shadow phase, what are the chances that every card left in your hand will be a vital one?
I dunno, I guess I just don't see the point in playing the card unless you plan on making use of the move limit bonus. Giving the other player 6 cards is pretty much never going to hurt them unless you're trying to mill their deck away (in which case you're probably playing Dwarves instead of Rohan anyway).
To answer your question for the thread, I'd draw 6 cards, every time. =P