As my planets have started getting developed, they have a need for ever larger work forces. Additionally, I have some far flung colonies that I am trying to bulk up. Those are set as destinations, and everything else as sources.
Close to Earth, I have a few worlds with substantial excess population, and a few worlds with huge worker demand. I don't necessarily want fast immigration OR emigration from those worlds which utilize their workforces; but I would like worlds without the utilization to supply the colonists to the distant planets.
Setting some sort of immigration\ emigration flags would be helpful here. Maybe a priority button in the civ\ind so i could set earth to a low priority destination for colonists and Mercury to a high priority source for colonist, allowing you to drain citizens to more distant worlds. As it stands now, what I usually do is drain all the colonists from mercury to earth, revert mercury to a destination, and they all come back to mercury! A money maker to be sure, but not how I want to use those people.
Heres another example: I have an population farm, an industrai world and a research world in one system. The research world needs a set workforce, but only needs to grow at its natural rate. The industrial world needs bodies. Lots of bodies. Set the industrial world to destination, and the other two to source, and the research world drains of people. Set the research world to a destination, and the population farm populates the research world. At the end of the day, I still dont have bodies in my industrial world and run a worker shortage. I can set up a fleet of population movers I suppose, but its pretty annoying.
I don't want to flag "never move pop" on a world, I'd just like to have some sort of input between on and off.