Tactically, Starboard has the option. If you're S and you're headed to the favoured side with a clear lane, you DON'T want Port to pull off a successful leebow and steal your thunder.

If you're the Port boat and you don't want to tack into the traffic or risk the foul, it is polite to ask for the cross if you suspect Starboard is going that way for a reason. If you ask, you're obligated to tack immediately if Starboard says so, and hold your course if he waves you through.

Edit - Can't keep up with you, Eric. I disagree, however; I see this situation three or four times a season from both sides. Watch the latest video from Steeplechase for a great visual demonstration of how effective a leebow can be.