Three 'central' defenders places greater emphasis on few things in my understanding (which may be severely limited!!):
- The quality of the central midfielder in using their presence to physically dominate, blocking runs and passes and being able to play on the turn to shift defense into attack
- The tenacity and drive of the wing backs to get up and down the pitch. Emphasis on stopping crosses and staying wide to not infringe on the two 'outer' central defenders
- The organisation, communication and reading of the game of the three 'centre backs'. Not leaving people unmarked, communicating positioning and responsibilities at set pieces or in open play when in the defensive third.