I haven't tried it myself yet but from the results I've seen online it seems like a good way to decrease roughness. But you still you have to print with a low layer height since larger layers result in deeper crevices which can't be mitigated by the vapor. And its nothing I would try without proper safety measures. Of course you can also sand and polish your surfaces by hand but especially larger surfaces get really tedious really quick :D

I finally have a pretty well tuned ASA and ABS capable printer and am excited to give vapor smoothing a shot. That said, I am very curious how repeatable it will be in terms of part tolerance. Most of my parts are functional. Nicer surfaces would be cool, but not if it results in some variability in tolerance.