Since when? That was the whole reason for the initial switch from the 4-2-4 to the 4-3-3
Need to look at the team. Originally we had Pirlo as a creative outlet, and Vidal+Marchisio as hardworking midfielders who were offensively limited to compensate for Pirlo, but still managed to make offensive moves, cause we had Pepe as hardworking winger, and Vucinic who's off the ball workrate was greatly undervalued.
Without Pepe, we first switched to 3-5-2 to maintain a strong workload on the wing, with an improved defence, whilst allowing both cm's to make much more offensive moves.
With the breaktrough of Pogba, there was no path back, as Pogba needs to be able to press very offensively, and make offensive moves. Same with Vidal. They were allways a bit limited by Pirlo's presence, but not THAT much cause of the 3cb's and wingbacks.
Currently however there is basically what DelPiero84 explains pretty well. Marchisio is in the central midfield, so you take away a gab and replace it with an incredibly effective holding midfielder, that can cover quite a distance whilst keeping the tactics and shape of the unit in mind. This allows much more freedom from both CM's to go forward, wich we have been seen. Coupled with Tevez playing more cam/ss then actual forward, this gives a very strong central presence.
In order to have perfect balance, juventus would need the current midfield, would need strong cb's who can shine in a 4backline, and wingers who combine creativity with workrate.
Wich brings is to the topic from Berardi who can both play SS and wide. Berardi has alot of raw talent and a high workrate. I sincerely hope he's gonna break it and become consistant because he is SO perfect as a wide player in a wing based formation.