Originally Posted by The Witch King of Angmar
Thanks for answering that. Honestly, after hearing that, it makes perfect sense because you could send some of the small weaker spawned units to scout or do other meager tasks for you without much cost on your resources. However, what if you are running very low on resources, what if those auto-spawned units take them away when you need to devote them to something else or are they really just that little of a cost to create?
The units that spawn over time are free other than population, Wargs/marauders and I believe goblins are free and train over time automatically again, for free. You can also choose to turn their spawning off if you wish to save your population for other units.