Thanks SJ
I would think it would slow down the game a lot.
Imagine waiting for your population to grow to 50 million before the first facility can start producing.
And if you "unthinkingly" constructed 3 or 4, it could be years before they became functional by population growth alone.
I can see its attractiveness for realistic play. On the minus side, it would be just one more aspect of the game to micromanage (unless the computer gave a warning that it would be non-functional
).