In my first play through, I put a bit of effort into designing my bases in such a way that I could build large barracks and large vaults in the hope that their efficiency would make it worth the effort and initial cost... and I was punished for it. Since then, I haven't built them every again and I don't intend to. They are cumbersome, and not very effective.
In the early game, the up-front cost and build time makes them an unattractive option. You rarely need that much living space or storage space all in one shot, and it logistically difficult to 'upgrade' from the smaller building to the larger ones. The larger buildings are more efficient in terms of base squares and monthly cost; but the base squares doesn't matter much until the late game, and the monthly cost difference is not great... If you crunch the numbers, you find that it takes almost 2 years of full usage for a large barracks to match the cost of an an equivalent number of small barracks; and after that you'll be making around 14k profit per month - which is essentially insignificant 2 years into the game.
So, in the early game - they are a poor choice. The upfront costs are too high, the payoff is too low. But that's ignoring what is probably their biggest draw card: base size efficiency. They take up less base space than small barracks / small vaults. ... But in the late game, when base size actually matters, the luxury barracks and armoured vaults are superior. And furthermore, it is far easier to replace the smaller buildings than it is to replace the large ones. So if you build your base with large barracks and large vaults, then you end up losing out on base size as well.
So... for me it is pretty clear that the large barracks and vaults are a waste of time/money/space... Does anyone have any other thoughts on this? I'm thinking they should probably be buffed so that they are as space efficient as the end-game buildings. After all, it really does take some additional planning to use them at all. They need to be good to justify their use! (Or just remove them from the game and replace them with something else.)