My understanding is that it is the ability to simulate the games data driven systems.
Example: Designing an RTS you could feed in all the values, costs, speed, damage, health etc of both armies.
Then you can hit go and see who will win.
You can then use this to quickly balance the values to something fairer.
Now, I think thats what you do and why you do it.
But I don’t know myself HOW you do it.
I would imagine its all sorts of fancy excel sums…
I too would love a good guide…