As we are no longer clogging up Hellkites shipyard thread I will elaborate on why MVAM is a silly idea from an engineers perspective.
1. Weak points. When the ship is combined into one unit *stuff* needs to be able to pass between the hulls. This means that you have corridors, turbolift shafts, power conduits, data lines, air lines - all sorts of things between the decks. When the ship is separated these all need to be sealed off, but by necessity they will go right up to the exterior hull, so the plane along which the ship is docked will be littered with access points. These won't be heavily armoured (they can't be), so you have a deliberately designed in weak point in your combat ship (great for plot lines, not so good for combat).
2. Wasted space/mass. Because your ship is actually three ships, it needs three of most things. Three warp cores, three sets of nacelles, three bridges, three life support systems etc. You could claim that this is good redundancy for a combat ship, but then you may also need spares for critical systems (so each segment may have two life support systems). A number of these systems will not be needed when the ship is combined, so the ship is always lugging around wasted mass and space (a combat ship with space to waste, shocking). In addition there will be elements situated on the join planes, phasers, shield grids, transport emitters, sensor arrays, armour - all stuff that is completely useless when the ship is combined.
3. Ship loss. What happens when one of the segments is destroyed? Are you left with two thirds of a ship? Can the ship operate with a segment missing? The full ship is left with lots of bits exposed (see point 1).
4. Mechanical failure. What happens if you can't redock the ships... You are left with a fleet of small ships instead of one larger ship. But if the small ships can operate perfectly well independently, what was the point in making so many compromises docking them in the first place? Is the whole crew scared of transporters?
Now that said, I do like the idea of emergency saucer separation where the saucer can act as a lifeboat in the event of a catastrophic failure (aka Generations). And if you are going to insist in taking your lumbering cruise liner full of children into dangerous situations (I know, just for laughs lets go into the Romulan Neutral Zone) then using it to leave the civilians behind also has a certain logic (but if the ship is expecting to go on missions like that it shouldn't have any civilians!). But I certainly don't agree with using it to "give the Borg something else to shoot at." I thought it was Picard that didn't like children, not Riker!
