I've been playing my first game of Stellaris as a Xenophile empire, and since I didn't know what the pros and cons were I have been giving away Migration Access to other empires whenever the option comes up. Now I'm a bit further in, it seems to me that it provides a lot of benefits:
- You get population on your planets faster due to immigration (as long as they have compatible terrain) and you get to keep the generated resources.
- You "take away" population from other empires which weakens them.
- You can build colony ships using any of the race on your planets, which makes it easier to colonize other planets. This works best with Gaia planets since a variety of races will want to migrate to those.
I can't think of any downsides, but I'm guessing there must be some since I sometimes get a bartering advantage just for offering Migration Access. What am I missing?