There have been more than 20 Money in the Bank cash-ins ever since the concept was added to WWE TV back in 2005. Of those cash-ins, there have only ever been two that were made in advance, Rob Van Dam at One Night Stand and Damien Sandow on Raw.
Rob Van Dam did walk out with the Championship after he used all the power he had in ECW, but Damien Sandow's night didn't work out as well. WWE had the former star cash in his contract because they were trying to fight the ratings for Monday Night Football but that wasn't enough for him to be able to dethrone John Cena.
Braun Strowman is a heel now, there was no need for him to cash in his contract in advance because that would have meant him allowing Roman Reigns the time to prepare and it makes it more understandable if he loses the match.
If Reigns had faced someone like Kevin Owens inside Hell in a Cell instead then Braun in his new heel persona could have easily cashed in on Reigns at the end of the match so that The Shield wouldn't have had the time to make the save.
Interestingly, WWE has gone with Braun cashing in his contract in advance which definitely swings the match into Roman's favor. If Braun loses then they can also claim that Mick Foley had something to do with it, rather than having the Monster Among Men look weak and be pinned by Roman Reigns again.
It's obvious that WWE wants Reigns to have a lengthy title run but it appears that they have allowed him to face his hardest opponent first, because there aren't many men who could be seen as more of a threat that Braun and after this weekend Roman will have defeated both Brock Lesnar and Braun Strowman so where does he go from here?