Mancini does indeed want to try different formations because last season in some games the only plan we had just didn't work. Examples of this are Everton away where arguably referee decisions cost us but still we didn't play great.
I think personally 3-5-2 is a good formation and we have the players to suit it. Just today it didn't work against a very good Liverpool performance.
The signing of Sinclair will give us another option which I think is important and I really think he can be a good signing for us.
To the poster who said earlier about Yaya and how he should be playing a more attacking role. We don't have Barry available so that's why he is dropping back further. When Barry is back Yaya will be his awesome self again.
Working on a plan B, or C, just means you spend less time perfecting plan A. So while you play plan B badly against liverpool and throw away points, you'll also be that much worse at plan A in the next game.
Teams that want a plan B almost always screw up because there are so few times a plan B will work but trying to get one tends to screw up the team full stop.
It's just an incredibly bad idea, and your side doesn't suit it even slightly. Nasri was cack as the entire offence relied on him linking the game, and he was rubbish. Put Messi in there, sure, Silva, Nasri, are weak on the ball, girly, not fast, not powerful and Nasri in particular is such a selfish little twit. Without someone doing the running for those two, they are almost worthless. Milner is marginally defensive and can help a right back, he can't in any way do the right wing and right back job well, he can't do either very well and trying to do both he was terrible. Koralov and Milner didn't get nearly involved enough because they were too deep too often, there is a reason most teams play two players on the wing.... because it works.
Likewise CB you have 2-3 cb's who are excellent CB's, and haven't really ever played a 3 at the back system they were all over the place in all the games. It also relies on more CB's which means minor injuries will put you back into using Savic for instance a lot more often than if you play 2 at the back, and he sucks. Koralov is just rubbish, offensively and defensively. Because of the three in the middle of the park and wing backs that end up too deep it means either Yaya stays defensive because he's needed, which doesn't work, or he supports Nasri/Silva bombing forwards which the team needs.... but again doesn't suit the formation well.
City have looked significantly worse since they started peeing around with the system.
You use plan A, win 85% of the games, lose the other 15%, or have a plan A and plan b, you only lose 5% of games, but you only win 70% of games... and drop points overall, and end up a less good team. It basically never works. Worst thing a manager can do is try and make a second team for big games, it merely tells your players you don't believe they can play well enough in their BEST formation to win, so they'll try an alternative to try and not lose. mentally it undermines your players, and physically it means practicing more than one system, jack of all trades, master of none. You can not be as good in plan A if you're practicing plan B instead.