I'm a native English speaker and I usually turn on subtitles for media with English audio. Just because I understand the language well doesn't mean I'm going to

I'm a native English speaker and I usually turn on subtitles for media with English audio. Just because I understand the language well doesn't mean I'm going to perfectly hear everything that everyone says throughout a video. The character could mumble, speak quietly, have an accent I can't parse well, be speaking while something else in the video is making a noise, or there could just be something happening near me that drowned out a word. Subtitles are a good backup for when something inevitably goes wrong audio-wise.