From what others posted, the downside could be that there are SEO issues...having duplicate posts does not bode well in Google's search engine.
If one doesnt care too much about this, then I guess it is not relevant. I imagine any of the proceeds from being on STEEM would outweigh the potential loss of Google traffic. But then again, it depends upon how big a site is.
Hmmm, seems like it would be a minor problem, but the exposure gained might offset it like you said