Ranocchia +Bonucci was a great duo with clear strenghts that synergised so well, they erased each other weaknesses.
The only issue, like many times with italians, is that they shine in a specific system, and outside that, its alot less.
Think Zambrotta at juve, and at barcelona.
Ranocchia is a beast in anticipating and 1v1 in close quarters. He's pretty agile, quick and aggressive, but he's a slow runner. He's pretty bad in open space.
If you have well organised defence playing as a unit, and a defender that covers the space behind him, ranocchia suddenly becomes a monster.
Add to that his ballplaying capabilities and great aerial skills (wich we sorely lack tbh), and you see why conte wants him
Example :Chiellini and bonucci on their own, are average. Then you add barzagli who brings a brain to the defence, and suddenly you got potentially the best central defence in the world.
Conte is a master tactician. He has a different approach from the blatant idiot mazarri. Mazzarri never bothers that much with his defence. Plays ranocchia like a stopper without backup. Because he wants to get his fancy system in place.
Conte doesnt do that, he molds the system to get most out of his players, with an eye for perfect balance and organisation.
I'm confident, if Conte wants Ranocchia (conte must believe in the player), that he can let him play as if he was Montero, with twice the size, and half the lunacy/red cards