Well I've tried SW a few times, using Demichelis from River Plate. My impression is that if you've got a player with good off the ball, positioning, and relatively good dribbling, you can play 2DC+1SW (instead of 3DC) and leave him at the SW position, free role and hold on ball...
In 3DC formation the score of central DC is normally around 7.3-7.5 per season, but in my 2DC+1SW formation the SW can normally scores around 7.8-8.0. Hope that helps