I've been enjoying the game for a few days now, and just recently started to use the Design Units feature after getting my bearings. What exactly does the Hide/Unhide checkbox on the list of units do? I can see that if I check Hide it removes that unit from the list of trainable units. Is it purely for ease of selecting units from an organized list in case you make a lot, or does it do something more grand like prevent the AI from using units marked as hidden when you let the CPU use your custom faction?
I hope for the latter, but if not... consider it a feature request?