I was surprised Antonio Conte didn't introduce his 3-4-3 formation even earlier than he did this season. I just think he was waiting for a good reason to change to what he knows best.
It's not a particularly adventurous tactic because when Chelsea don't have the ball, it's 5-4-1. But when they have the ball, all of a sudden it's very attacking.
It combines two different ingredients: Italian catenaccio and the flair of the players going forward. For it to work, you need great players at the back and great players up front, and that's where Chelsea have an advantage over all their rivals.