Geez, didn't you read the strategy index? My Growth and Death by the numbers is there.
http://forum.shrapnelgames.com/showthread.php?t=35801
As the question itself, when do you get growth? Here's my answer:
1) When you want to pursue a high gold strategy and already have Order-3. Growth and Order are great together.
2) When you plan on recruiting a lot of old age mages.
3) When you plan on doing a lot of blood hunting (not some, but a lot).
4) When you've already taken misfortune, especially if you've picked up Turmoil for whatever reason.
Note, note all of these reasons require Growth-3, just some Growth. However, due to exponential population increases, you get more for your points buying the third point of growth than the first.