I think it refers to the units that we produce ingame. Each unit has corresponding number of supply, ie. Hobos has 1 supply value and Merc has 7 supply value.
With regards to the rewards for reducing the population, every time that you manage to destroy troops from your opponents gives you a reward of futures for your effort.
I simply say that with this initiative, they are promoting battles so as to get the drugwars more competitive and interactive. ^^,