Example: If a product's main feedback is auditory (ie. alarm clock, voice assistant) when is it necessary to give visual feedback (ie. LED indicator, display graphic)?
Sorry if I misunderstand the question, but I've been given little detail.
I would say always, because:
- People can have their sound turned off, because of their location or they forgot to turn it on.
- Some people are deaf and will never be able to hear the feedback.
You could also have a clear toggle button in your application or website to turn visual feedback on/off.