I should qualify this as more as a PBW/MP change.
It becomes a mad colony rush,. Check out
http://www.spaceempires5.com/en-US/node/2782. This old guide outlines how to pump out 17 colonizers by turn 11. So all these ships will likely find planets to colonize, no real thought on having to support them resource wise.
How do you counter that type of expansion other then being forced to follow the same path?