Lots of stuff flashing around, too fast to easily focus on.

: It's extremely common. A lot of people probably don't remember they even
: exist because they've had them disabled since they were introduced.

How common it is wasn't relevant to my rationale though. Even if practically nobody bothered to turn annotation on, I still wouldn't feel obliged to try and compensate for that, if doing a video designed as an annotated product. I'd only be interested in coping for people willing to watch the video properly.

: That's kind of the first rule of entertainment, though-- get their attention,
: then keep it.

I'd associate that 'rule' more with TV & film though. I wouldn't be too quick to follow TV/film norms in gameplay videos, which are a different type of thing in some ways (e.g. often being a handful of minutes long). It might suit folk who are out to try and maximize watching, but other people might prefer to give priority to the way they want things to unfold, even if that might mean losing some of the more casual viewers.

: He was only saying you shouldn't put essential information in them, though,

That bit baffled me actually, but for some reason I skipped commenting on it. I don't see the sense in saying you shouldn't put essential info in your captions. Essential info is the most important type! So if you consider your captions to be your guiding information source - as I surely do - any essential info should certainly be in them.

: and I don't know how they do things over there, but over here almost
: everything shown on TV has captioning embedded in it that you can see if
: you want to or need to.

I believe we have caption technology in the UK too, but I was thinking of a simpler situation in which that wasn't a factor. It's a red herring really, but if you want me to to add it into the picture, I can update my statement to the following: I'm pretty sure the makers of a TV documentary wouldn't spend any time worrying about what viewers will make of their programme if they've elected to watch with the sound and automatic captioning turned off.