What does get added when you enable each Story Event(Original, Shakturi, Shadows)?

I've been searching around and I dunno how these affects a game

<t> Hi, I'm new here, I just got the game together with Sots 1 and 2, and also just bought Stardrive last month, and Kerbal Space Program, I also have played GalCiv 2 in the past and just recently, as you can see, I am very much addicted to Space Games, especially 4x games, at the moment. with KSP ...