So a few years back, in a time I prefer not to remeber, Milan fans had the pleasure of witnessing Leonardo's majestic 4-3-3. The thing about that was it wasn't very majestic, and the penchant for conceding, often minutes after scoring, was the downfall of this system. In Leo's 4-3-3, the team often looked more like a 4-2-4 and strikers like KJH, Pato, and Ronaldino did little to nothing on the defensive side of the ball. Devoting three players to the attack is difficult enough, devoting four!? That was the beginning of the end. The problem is Milan's Management never learns, instead of buying useful defenders and midfielders, they keep on buying attackers and with the current glut: Pato, Robinho, El Sharaawy, Pazzini, Bojan, and Niang. Playing more attackers seems to be the only way forward, even if it wreaks havoc on balance.
It's no secret, I don't like the 4-3-3 as an everyday formation, sure if you are chasing a match, with a few minutes to go you can chance it. But as a Coach presented with an opposition in the 4-3-3 I often salivated at the prospect of tearing apart the space left in the midfield. General school of thought says matches are won in the midfield and most teams deploy four if not five players in that role, so starting with three presents an immediate numerical advantage for your opponent. This can often be overcome with industrious workhorse type midfielders and wide attackers who are not afraid to get their "hands dirty" but Leo's formation did not have these sort of players. Allegri on the other hand has always seemed to get players to do a bit more defending, if not they are shown a place on the bench. With this said the 4-3-3 of the last three weeks seems to have made some progress.
The important function has been the inclusion of busy body Urby in the attacking line and DeJong in front of the defense as an defensive anchor. While this formation requires extensive time and understanding to achieve success, brief flashes have been seen in the last 270 minutes of football, but this is still a work a progress. Another successful point to note has been the willingness of the wide attackers, who are not truly "wingers" in the classical sense, to drop in and contract and congest space when not in possession. This was a detriment to Leo's deployment, as the statue of Ronaldinho stayed high and wide on the left and the traffic cone KJH or Pato, stuck high wide on the right. A shining example of this done correctly was Inter's Treble season when players like Eto and Pandev worked their tails off to fill in space making the team look like a 4-3-3 in attack and 4-5-1 on defense.
As I stated earlier this isn't for me, but on a striker heavy roster, with relatively young players not necessarily stuck in their ways or steeped in lazy habits, what other choice does a Coach have? He won't get credit for this transition, his detractors have already dug his grave, but take a minute and consider the level of effort required to teach, learn, deploy and function in a new formation, if you think it's easy you may want to step away from the video games for a bit.