Growth[]
Your growth level determines how much your GDP will raise next turn, which in turn effects how much money you get. The key factor is growth is stability. With high Stability maximum growth per turn is +5 and there is maximum decrease but there are many factors which will negatively affect growth: territory acts as a soft cap on GDP and for every 500 GDP over your territory you lose 1 growth per turn, having less oil supply than growth you will lose some growth, having a low stability will lower by growth by up to 5, and having a high growth will result in negative growth from "unsustainable growth".
Effects of Growth[]
Obviously enough high growth is better as it raises your GDP and in turn gives you more money to spend. The natural maximum growth is 68 growth (at which point you will gain 5 growth per turn from high stability, and lose 5 from "unsustainable growth".
Growth Decay
Your growth decays linearly and it is described by the following formula: ( ( X / 20 ) - 1 ) ^2 where X stands for your current growth. Less than 39 growth will result in no unsustainable growth.
40 - 48 = 1 unsustainable growth
49 - 54 = 2 unsustainable growth
55 - 59 = 3 unsustainable growth
60 - 64 = 4 unsustainable growth
65 - 68 = 5 unsustainable growth
69 - 72 = 6 unsustainable growth
73 - 76 = 7 unsustainable growth
77 - 79 = 8 unsustainable growth
80 - 83 = 9 unsustainable growth
84 - 86 = 10 unsustainable growth
87 - 89 = 11 unsustainable growth
90 - 92 = 12 unsustainable growth
93 - 94 = 13 unsustainable growth
95 - 97 = 14 unsustainable growth
Sorry for the gap but I don't really linger here.
103 = 16 unsustainable growth (I have literally never seen anyone have higher growth than this)
121 = 22 unsustainable growth