But don't even think of these buildings in terms of what the slaves can do for you if you lose the settlement. That's really the most minor of minor benefits that these buildings can do for you.

The main reason for them is to allow you to recruit troops from that area to fight for you. Like your factional MICs, the range of troops that you can recruit will vary from province to province. Use the recruitment viewer to work out which "foreign" troops you want and where to get them, and then build up these buildings in those settlements.

The government level determines how high you can build up both your own and your foreign MICs. The key number to remember is that you get 7 levels per government. Level 1 government gives you 5 levels of local, and 2 levels of foreign MICs, level 4 gives you 2 levels of local and 5 levels of foreign MICs. Of course level 2 and 3 governments are in between.

The range of "foreign" troops you can recruit usually (but not always) expands the further away you get from your home territory. And of course the high level MIC you build the better troops you can get. Keep in mind that in some areas you can't get betters troops beyond level 2 or 3 MIC.

One exception to this is foreign generals. These can always be recruited in any province with a level 5 regional MIC. Of course to get this you need a level 4 government.