At what quality of a CDP negates the use of a DAC?

Hopefully this is a straight forward question? I know that our ears should be the final decsion maker but is there a general philosophy about at a certain quality of CDP, negates the use of an external DAC?
I would guess when the internal dac exceeds the quality and sound of the external add on dac. It really depends on what you are comparing it to. I am often surprised by the number of people who use external dacs with the idea that by using an external dac, by definition, is superior to a one piece CDP. I think that one should compare different options, including budget, need for interconnects and other ancilaries and make a decision.