I was watching an episode of Doctor Who today while riding my bicycling trainer. When I do that, I tend to leave the subtitles on, just so I don't miss something if I'm busy messing with the wireless headphones because of sweat. At one point, Donna and the Doctor are communicating through windows and the subtitles state [no audio]. I've seen it before where the subtitles tell me what music is playing or what sound has just happened, but [no audio] was new. It didn't occur to me that you might want to let someone who couldn't hear know if it looked like someone was talking when they really weren't.
I think sometimes my product has similar issues. Several times recently I've found myself asking a designer, "How do you cancel?" Or, "How do you undo that action?" The answer has been, "There's no need. They can check in preferences." or "They won't really do that in the first place, even though we let them." Ugh. As a user, I always want the ability to say, "No thank you, not right now." And, even better, "Not right now, and quit asking me; I'm sick of pushing buttons." If you're doing something for me that I can't see, such that it's buried in a preferences menu somewhere, it's even more imperative you give me a way to bypass it without digging around the site map. [No audio] reminded me of those recent issues because you should always be thinking about the cases where you account for something someone may expect, but which doesn't happen and all those other use cases that just don't seem obvious because you want to provide a specific piece of functionality and your ego is potentially tied up in how users will use it.