At work today (I know, I know- I should have been working
) I was trying to think of a better way to answer your question LSP.
I think the graph below, depicting the start of my turn 3, shows the value in having the formation with all of its detachment support.
My Greatsword horde could realistically deal with two of the three nasty blocks facing it in the front (Blackguard, Hydra, Corsairs) in combat at one time. Fighting all 3 at the same time would probably wipe out the horde in a few combat phases. No matter how many I was fighting, if the Cold One Knights came flying in from the flank you could just forget it- game over.
If the Cold Ones had severely wounded the STank on the previous turn, I would have shifted units labeled 1, 2, and 3 towards that side to keep the Knights off my flank for 3 rounds (using one diverter per round). The Luminark, labeled 4, would have been a last ditch effort if my horde was depleted to the point it could not take on the Knights.
Which means I could have avoided a fight with his killy knights the rest of the game. After shifting those diverter units over, I would have pushed my horde into the center to force the start of combat and used my last archer unit (like I did in the game) to get in the way of the Blackguard to keep them off my Knights and out of combat for one turn.
My Knights, on the other hand, finished off the DE Warrior tarpit by Turn 4, and had they caught it, could have potentially gotten a rear or flank charge into his battle line on Turn 5. Most likely he would have used at least one of his harpy units to stop my left Halberd detachment and would not be able to stop the Knights from eventually joining the center fight.
The best thing I can say in defense of the formation is that it gives me many options, especially when I am facing lots of stuff I don’t want to fight at the same time. I can quickly swing them to where they are needed, as depicted in the example above.
The points I lose to buy time are not that great- 120 for stubborn Halb detachments, 80 for the Archer parent, and 35 for the Archer detachments. They allow my 430 point Knight block and 573 point Greatsword Horde time to work their hatred on the enemy.
Hope that helps.