It's faster for the crew to get on and off the wire during gybes. I like driving downwind from the wire and do it quite often in distance races...but it's really hard to not get twitchy with the tiller when going out and coming in and gybes are tough to get smooth when you have to coordinate it with going in and out on the wire. AND you can get more mass further back on the boat with the crew out. He/she can use the skipper's trap and trap out behind the skipper (on the stern if needed). The crew can't position his weight behind the skipper's position if the skipper is out on the wire.