There is nothing wonderful about it. In vanilla, when you enslaved a settlement, the game would place a trade resource for the slaves and the population in your governed settlements would increase. The same process is happening here, but instead of slaves we've re-invisioned it as refugees, so instead of a slave resource it is a refugee camp. The same process is in place, but instead of slaves increasing the population of your governed settlements (which is silly if you think about it - the population can only really represent men of a military age rather than the entire population) it is refugees from the newly conquered province.

Foot