I think that there must be always some sound/information going around in a video, otherwise it's the same crap that makes you sleep during classes*, if there's music it should be atleast mached to the video, it should also be not too loud, overpowering the video with varoius sounds makes it hard to concentrate and understant the information within the video. Having no sound whatsoever is just as bad, it makes the video awkward and uncomfortable to watch, playing your own music during that kind of video just adds to the inconvenience.
I hate it when i have to mute/downvote a video but sometimes it just has to be done.
*when the subject is so boring that your brain goes to a " brain fart " mode.