Well I normally play with agricultural civs on Deity, and by the time this Great Wonder appears most of my cities are fully grown to size 22 plus. So the few times I've built it, it makes my citizens grow at double speed when the granary fills up the population grows by two instead of by one point. Although this might sound good, it isn't. Because this wonder comes in so late; by that time I have all my cities carefully micromanaged and popping two citizens every now and then (being agricultural makes it even worser because of the fast growth rate in C3C) very soon they start rioting or camplaining and it's a continous micromanagement to keep them happy. You have to do many readjustments continously and when doing so with 70 or 90 cities can prove a real burden, at least for me. I suspect others would disagree with me because perhaps they are more patient or are aiming to score high. I only play to win (and have fun), not for score or milking, so the size of the population is not an issue for me.
The only time I've found it useful is if you are intending to score high and you've captured lot of land and want the pop to go up asap or else you're expecting some Nuclear Strike. Other than that, I wouldn't recommend you to build it. I always skip it.
But every player has their own style and that's what makes this game so cool and addictive.
