The change of formation was kind of forced with the injuries/suspensions but credit for Allegri for going for it in a crucial game.
Every manager should base their team around the best players in their squad. 3-5-2 was a result of Conte wanting to fit in Vidal with Marchisio and Pirlo. There is no need to continue with it given that our midfield is our biggest weakness. I'm glad Allegri found a workable solution and one that has flexibility to fit other players (e.g. Pjaca or Marchisio).