You know .... I don't have the documentation in front of me ... but that code provision sounds a lot like my writing .... it might have come from one of my proposals.
There was a time when some folks, especially at certain other "inspection" forums, would get all huffy if they found a circuit with a selector switch supplying both the heat and the AC. Or, if they found a duplex receptacle supplying the furnace, or if the humidifier built onto the furnace was powered by the same circuit, etc.
The NEC 'dedicated' circuit requirement comes after decades of the requirement only being found in the Mechanical code.
