For me, its contextual-- Blades in the Dark is probably trying to simulate the literary device of a flashback as its used in a heist movie, you see the thing happening and either a suspensful question is posed (did that person really die? why is the person doing that? how'd we end up here? is this really it for our heroes?) and then we're shown the parts of the story that answer our questions. It builds tension because when we lack the set up, we don't know all the information that might reframe the events.
Basically, its a way of building towards a 'conclusion' when that conclusion takes place before its consequences (the heist itself,) by framing it this way, we get a standard build up of tension, followed by a pay off that answers the questions being posed by the action. The flashback itself is a way of ensuring the Questions precede the Answer in the telling of the story, when preparation definitionally takes place before the thing being prepared for.
So, "Did Rodney really just kill Joey and betray everyone, is the heist a failure, is our hero dead?" is a question that allows the preparation where "Rodney and Joey faked Joey's death to gain the mark's trust, and are using that to turn the tables and pull off the heist" to function as a plot twist, and a payoff for the tension build up, even though Rodney and Joey preparing the trick takes place before the scene where Joey is seemingly shot.
Great Pretender on Netflix is an excellent case study of the technique.
BITD is cool for including such a storytelling device as a mechanic, because its basically the protocols and techniques for TELLING heist stories and similar fiction projected onto a roleplaying game. I'd love to play it sometime, but it might not be appropriate for games that aren't after the dramatic trappings of a heist story, but the activity of planning and executing a heist, the flashback technique is dramatizing. That style of play would demand that we know what preparations were made before the moment they're preparing for because it would be measuring skill as forethought on the player's part, in the same way pulling off a heist would require forethought on the part of the participants.