Dominion question.

[Borg]

I'm an old strategy gamer but new to Dominions.
I downloaded the demo Last week and have been getting into the game headfirst .
I have to admit, this game seems to go "deeper" than any other TBS game I've played before.

So far I've been absorbing (reading) all the info I can find on "how to play" this game but there's one subject I have found very little explanation about. And that is the "dominion" factor itself.

Would anybody please care to point out to me why "dominion" is important ?
Why would I ever want to have a Dominion of 8 or more , why is a Dominion of 1 or 2 not enough.
In short, I'd like to know what effects Dominion-level has on the game.

Thanks for your help.