WWE has wanted Roman Reigns to be the top guy of the company for a long time. This is evident in a lot of obvious ways. As much as WWE tried to make Roman Reigns a widely received top babyface, there was still considerable resistance in many of the markets WWE travels to.
But The Shield is a money idea and it's one that WWE has been holding in their back pocket since Seth Rollins broke up the "Hounds Of Justice" so many years ago. WWE might have figured to make Roman Reigns the top babyface, but he needs to have his brothers by his side.
This reformation of The Shield could cement the future for Seth Rollins, Dean Ambrose, and Roman Reigns to share the role as the top face of WWE.
If they go their separate ways again, WWE could simply write it as a brotherly parting instead of a ruthless betrayal. All three of these Superstars could use this status to dominate the top slots in WWE for the remainder of their time with the company.