Conte prefers 3-5-2 in Italy because it helps us keep possession. Even if that possession is mostly around our back line, it's still possession. And we control 90% of the games we play. Last year we started 9-1-1 too if I'm not mistaken. I mean, we still pick up a ridiculous amount of points with 3-5-2. However, there are games where you know right away that it won't work. That is when we have to change formations. Conte needs to recognize it faster and adjust accordingly.
I honestly understand the 3-5-2 preference in Serie A because the game is slower and teams are reluctant to press us instead hoping for counters which the 3-5-2 holds up better against than a 4 man line when the fullbacks push up.
In Europe, it has to be 4 man back line every game.
Edit: One thing I'll say about the 3-5-2 and our play in general is that it is very, very structured and rigid. I don't think Conte allows much, if any freedom in our attack. If you just watch our corner kicks vs. Madrid. Obviously he instructed us to just pass it back to avoid counters.
Our 3-5-2 attacking is extremely rigid, the only player that makes any sort of movement is Tevez, the rest are nailed to their positions. You will see players sometimes stray into an area to make a tackle and then immediately sprint back to position instead of pursuing the play.
You will never see a wing back drift inside or exchange positions. If you actually watch our player movements every game, you will start to see very distinct patterns that are very predictable.
For example, our CMs always position themselves on the corner of the box and in build up they will often drop in between the wingback and the CB on that side.
Our second striker will always look to get played into feet on the edge of the box after he runs across the target man. Our CBs will always take their space when Pirlo is man marked and find themselves in midfield. Our wingbacks will always pass back inside. Our CMs must always fight like dogs to sprint back and cover Pirlo's sides. Not allowed to stay up for even 15 seconds. Target man has to always push up as high as he can to draw at least 1 defender, he never makes a diagonal run. You never see long through balls to strikers, they always go to CMs, if we ever play them. Could go on... I'm sure opponents have recognized these tendencies by now.