#1 It leads to Edge winning the World Championship

The story behind the main event of WrestleMania 37 was the emotional journey of Edge's return. However, this story didn't have the ending he would've hoped, but a new chapter can start at Money in the Bank if he wins the briefcase.
If history is any indication, Edge will not be handed another shot at the title; he'll have to earn it. The most fitting way to do that is to win the MITB contract.
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Although he may have many more World Championship reigns, his 12th reign would be historic. It would come after a lay-off of at least a decade, and it could be his final reign. It should come about the same way Edge won his first world championship, i.e., by cashing in the MITB briefcase against a weakened champion. Such a moment would produce feelings of euphoria and Deja Vu.
Becoming Mr. Money in the Bank accomplishes exactly what Edge wants. It essentially guarantees him a future World Championship opportunity on his terms. This was his primary motive for returning, and winning the briefcase becomes a massive stride towards accomplishing that goal.