Hi Xanadron,
Other people can correct me if I’m wrong, but the short answer is yes, the engine only includes the content that it needs when packaging.
The short version of how I understands that it works, is that the maps (and other assets) you specify through the ini files (or through the command line) are marked for cooking and then it also cooks any referenced assets (which pull in any assets that those reference, etc.). The only exception to this rule is the Content/Movies folder, which it simply does a full copy of for any packaged platform. I’m unsure if there is any documentation about this.
Hope that helps. Cheers,