According to ESPN:

Greatest advantage: Size and versatility. SIXERS going to turn back the clock and roll out an enormous starting five featuring 6-foot-10 Ben Simmons, 6-foot-6 Josh Richardson, 6-foot-9 Tobias Harris, 6-foot-10 Al Horford and 7-foot Joel Embiid. That size will translate to a defensive identity. With the addition of an elite defender in Richardson on the wing and Horford and Embiid anchoring the frontcourt, the 76ers should jump from No. 14 into the top five in defensive rating.

Although there are questions about the Horford/Embiid fit, the addition of the former Celtic gives head coach Brett Brown an insurance policy when Embiid is out of the game. Philadelphia has the flexibility of putting Harris at power forward (his true position) to pair with Horford. The same holds true when it comes to moving Richardson to small forward, a position he has played the majority of the past three seasons.

Biggest question: The promise of this starting five comes with uncertainty about how it all works. Harris will revert to small forward, a position he has not played consistently since his rookie year. Horford is sliding back down to the 4. And although this group can defend, who will close at the end of games with Jimmy Butler and JJ Redick gone? In 12 2019 playoff games, Butler led the team in fourth-quarter scoring (6 PPG). 

https://www.espn.com/nba/story/_/id/27434744/big-questions-greatest-edge-seven-nba-title-contenders