So as far as I understand you need to spent your own population to build ground troops. If true than that means ground troops are insanely valuable and that losing them is the same as basically losing portions of your empire.
However, I still have some questions about how land units work. For example, if I build a transport and convert 1 population into a army unit, then will the planet just replace that population unit with time by making the population grow again? If so does that mean that it pays to have land units ready in advance so that once a war happens you won't suddenly have to deplete all your colonies of population?