They are intended for people with low vision to be able to "watch" movies. They're also useful when you can't actually watch a film, but want to "see" it.
Think of it as an audio book of the film...
Descriptive narration audio tracks?
Re: Descriptive narration audio tracks?
MakeMKV Frequently Asked Questions
How to aid in finding the answer to your problem: Activating Debug Logging
How to aid in finding the answer to your problem: Activating Debug Logging
Re: Descriptive narration audio tracks?
The relevant Wikipedia article, which includes some history.
https://en.wikipedia.org/wiki/Audio_description
https://en.wikipedia.org/wiki/Audio_description