Holding prisoners is a powerful way of hurting an enemy's economic power and for some races a great source of income.

If you can grab 100,000 enemy prisoners and hold them on a base you will inflict a minus 50 point happiness decrease on all the enemy's bases 30% of the time. If the enemy has a PC rating of over 40 (like the Solar Federation ) you will inflect a 50 point happiness drop 100% of the time on that enemy. If you can place over 100,000 enemy prisoners on 6 different base you will be delivering a minus 300 happiness hit to all the enemy bases every turn. This will grind your enemy into to an economic meltdown.

Lizards sell all the prisoners that that capture at the asking price of 2.2mc for colonists, 8mc each for crew, 12mc each for troops and 125mc each for highguard. Robots use prisoners as food for their insectoid nests to grow more insectoid natives. Stormers and EE are especially well adapted to capturing prisoners, who can be put to work in labor camps / mines.

Keep prisoners off worlds where there are useful structures as they regularly destroy these in riots. a few hundred troops of yours, and a few dozen HG, on prisoner worlds to reduce frequency of riots from 75% to just 50% of turns. The enemy is sent the location of where the prisoners are kept.

Borg and Robot prisoners are useless, they won't work in prison camps / mines.

The best way of capturing enemy prisoners is the use a force made up of mostly high guard and weak ground assault units.

After ground combat is all over the strength of the two remaining side is measured and the side that can best the other side by at least a factor of 300% captures the other side. This is how the strength points are calculated: