On the mission 'The Attican Traverse: The Rachni' at the end of the mission you are faced with the decision to either free the Rachni Queen or leave her to the fate of her malevolent offspring. Given the variety of possibilities, dependent upon whether you've imported saves from ME1/ME2, what are the various possible outcomes of this decision? Also, what war assets will be gained or lost as a result?

I'm currently playing ME3 with a brand new (non-imported) character and it seems that the past history given to the player by default indicates that you have presumably killed the Rachni queen in past experience.