A hero under your control (no matter what level) consumes 10 points of karma.
Every settlement level requires 10 points of karma (i.e. possessing a village consumes 10 karma points, a town consumes 20 points, and a metropolis consumes 30 points).
There are 3 separate karma counters for heroes, machinery and settlements. Having 50 karma you can control 5 heroes, 1 metropolis and 2 villages.
In case if your karma decreases and some of your heroes/units do not have the sufficient amount of karma provided, you lose control over them.
This means that you still own them, but you cannot move or attack with them.
Galeons, cannons, headquarters require 10 karma points. All other types of machinery require only 5 points.