When comments are enabled on free-form ads, there's an increase in community engagement, Reddit claimed, without indicating whether that increase was positive or not.
I remember a long time ago, like maybe a decade or more, the regular we-can-see-they're-ads ads on Reddit could have comments enabled if the ad buyer wanted. I remember jumping in on a few of them and they actually weren't bad, at least in the ones I went into (a biased sample to be sure). If the ads weren't obnoxious or misleading I could see it going not too badly.
At some point adblock got good enough that I stopped seeing ads on Reddit any more, though, so I don't know when they stopped that practice.