Live video or audio chat is basically the only time you do want this. Granted, that’s a big chunk of microphone usage in practice, but any time you are doing higher fidelity audio recording and you have set up the inputs accordingly you absolutely do not want the artefacts introduced by this cancellation. DAWs, audio calibration, and even live audio when you’ve ensured the output cannot impact the recording all would want it switched off.

Default on vs default off is really just an implementation detail of the API though, as you say.