The other day, someone asked Google's John Mueller if adding structured data can potentially lead to less traffic from Google. The user showed a picture of featured snippets, because we hear markup may impact featured snippets in Google. And if you do not want to show up for featured snippets, don't include the markup.
First, markup doesn't seem to have any impact on featured snippet, so forget that for now.
Second, John Mueller said it does not lead to less traffic. He said "no" in response to the question. Here is the set of tweets on Twitter:
Don't you love the hashtag use here?
There is really no good way to measure this, but I suspect Google is measuring clicks on those featured snippet boxes. So I do trust John Mueller from Google when he says that.
I also know some SEOs have some evidence showing it leads to more traffic. Someone should do a big study on this...
Forum discussion at Twitter.