50% intelligible is not infinitely better than 0% intelligible. In fact it could be that you're completely misled into believing something that's not true at all. Whereas if you are aware you understand 0% you're not jumping to these wild conclusions as confidently.

For context, I'm watching videos of a guy making jet engines in his garage. The consequence of being mislead is about zero. I'm not concerned about the 50% I miss. There are no wild conclusions being jumped to. If anybody jumps to any sort of wild conclusions on the basis of a 50% intelligible video, that's squarely on them.

Unless the unintelligible 50% happen to align to appear intelligible... but wrongly:)

Idk, my English is not great but apparently I am better than YouTube subs because when I need help understanding an English word it turns out YT can't transcribe it either :/