But didn't we have all players back under Rafa as well? I don't know who it was (my bet would be it was HBHR), but someone made the point that it can also be an advantage having the players back and then streaming forward once the ball is retrieved. Some of the best goals we've scored from defending a corner are those where players were rushing forward, were found by Pepe and with two or three passes we scored the goal.
I'd say the chances of a successful counterattack decrease if you have all players back. If we clear the ball in the box, we have no one outside able to hold on to it and bring the others into play. It's more likely to go to the opposition, who can then put us under pressure again. Either with a cross into our box, or they'll have an easy time circulating the ball - none of our players can put any pressure on if they are over ten yards away.
I can't be sure that this is the case, but it's my guess. We have scored a goal or two (or perhaps more), but then again, loads of teams who don't take everyone back has done that as well (I hate to bring them up, but the mancs scored a great goal last season - or the season before - against Arsenal where Rooney got hold of the ball inside his own half, and within two three passes they had scored). Defensively it could also be an advantage if we don't have everyone back. Cruyff - when he was at Barcelona - left three, four players on the halfway line, so their own box wouldn't be overcrowded. All opposition teams had to remove three attacking players from Barca's box to cover for those players, and Cruyff felt it was easier to defend corners with fewer bodies in there. It makes sense to me - less chance of a "pinball" situation, less chance of a defender getting blocked out - but I'm not even certain that they used this tactic, it was only something I read once.
The most important thing though, no matter what system you use, is this:
It's about players doing their jobs.