I think the MVAM could have it's uses in instances where a ship is performing one assignment, but then something happens nearby which makes the Prommie the only local ship that can respond, but can't abandon it's current task.
Consider this example. Our example ship is delivering desparately needed medical supplies to a planet, who's people are dying in droves every second that is delayed. Now as the ship enters the system, they recieve a distress call from an outpost in the vicinity, under attack from pirates, threatened by stellar phenomena etc. The outpost could be saved, but only if the Prommie immeadiately diverts to assist. If they divert, many people will die on the planet.
Now, if this ship were a normal, single-hull vessel, the captain is restricted to a single choice, save the outpost, or save more sick. What's a captain to choose. If, however, our vessel is a Prommie, it's easy (or at least relatively easier). Simply split the ship, having the section that's least capable or useful to the assignment of saving the outpost carry on to the planet with the medical supplies, and letting the other sections go off and deal with the threat to the outpost.
I'll admit now, designing a ship for these kind of eventualities is a bit 'all but the kitchen sink' approach to design, but you never know how often this option could be useful, especially with vessels operating a long way from any kind of support.