You learned something different then because this finding is that some kinds of additional roughness delay the transition to turbulent flow which is pretty clear in the article.

https://phys.org/news/2014-01-smooth-rough-surfaces.html

A quick search looks to show the same general topic from more than a decade ago. I too have a recollection of this being discussed in the late 80s or early 90s. Maybe some folk wisdom that's just now getting quantified.

Thanks for clarifying.