From the point of view of how to go about taking on Real Madrid, I'm not sure I really see the point in changing to 4-3-1-2.
Sure, I prefer a back four - especially when taking on a team with wingers - but it is another system where there is a good chance of being overrun on the flanks.
However, if the 4-3-1-2 is just Conte adapting to the players he has available (i.e. he doesn't trust anyone other than Lichtsteiner to play right wing-back) I would understand the change.