#2 Accommodate many defensive options in the starting lineup
Chelsea have no dearth of defensive options in their squad, but they lack experience. This means that the more the number of players Lampard can accommodate at the back, the better the quality of the defence.
Andreas Christensen has found his much deserved place in the squad since the arrival of Lampard and the departure of David Luiz and Gary Cahill. The Danish centre-back was not favoured by the ex-Chelsea boss Maurizio Sarri.
Kurt Zouma, Fikayo Tomori and Reece James return to their home club after successful stints on loan. Meanwhile, Antonio Rudiger who has been Chelsea's main defender for the past two seasons is returning from injury to play his first game this season.
With the quality and number of defenders in the squad, the Blues can field two different formations with two different sets of players.
The only way to accommodate all this talent is to play a three-man defence with two full-backs playing as wingers, which instantly impacts the defensive. Considering the defensive form of Chelsea right now, they need as many players at the back as possible.