Its complex to explain, alot is going on.
Central defence keeps deep position, so do fullbacks who arent there to make interceptions but holding off players. The central midfield works as a team, as they rotate 1 or 2 pressing player whilst the third keeps the shape. Very important is the second and third most offensive player, who also has do to pressing.
In this way, you got 5 players holding off (defence+cheesio). If someone challenges marchisio, a central defender steps out, as Max controls the space in such a way that we controll the small space. The cm's hold the position and make sure we circle towards the ball as a unit, keeping the controll of the small space. The offensive players rotate the actual pressing.
Barcelona game was a masterclass on how you can do this efficiently to conserve stamina by swapping wich players hunt the ball and who keep the shape.
But here is the deal. Max his sucky milan, had shit individual quality. Wich got exposed back in Nou Camp. At juventus, your flamini becomes Marchisio. Who can suddenly pull of quite the lifted trough ball. Pogba instead of Muntari, so you got a black guy that can play football and win standing tackles+headers. You got a morata instead of Niang, so you dont miss THE FUCKING OPEN CHANCE TWO SECONDS BEFORE MESSI SCORES ON THE COUNTER, you got Tevez instead of el kebab. You got wallzagli, chiellini or bonucci instead of mexes and some cunt.
Allegri got alot of individually superior players compared to milanshit that nearly eliminated barcelona. And boy does he know it