Google indexes the content of the transcriptions and includes that in the algorithm. It might not a make a massive difference, but at this point it certainly can't hurt. I transcribed a couple of my vids and noticed that those do get played with the captions on in Vietnam, of all places. (I make low carb cooking videos in English - go figure!) My vids that don't have captions yet don't have those out-of-country views those with captions do.
I think that if you don't upload your own transcriptions, then it's probably wise to go in to the automatic transcriptions and edit them to make sure your keywords are spelled correctly. At least that way the algorithm knows your video is about "low carb recipes" instead of 'low CAR recipes" like mine always autocorrect to. Which puts my video in an entirely different niche if Google is indexing the captions. LOL
Just my thoughts, anyway.
Edit to add: I also include captions because I have a very thick southern US accent and I talk fast, so it might even help native English speakers figure out what I'm trying to say! Ha!