In most civilisation- and city-building games, nothing ever gets built unless the player specifically orders it. While it is simpler to depict the resource management in this way, it is very unrealistic to, for example, have to build "state" stables and "state" smithies in order to recruit knights in a medieval-themed game, or have to specifically order a resource extraction operation rather than have an autonomous agent do it in response to increased demand. It also prevents poor AI from sapping all your resources into pointless crap. Examples of Command and Conquer Economy include: