It all depends.
I had a client do a cryptocoin brand ICO and got enough sign ups to be worth $10k . Major ROI
With the news my team wrote, we've gotten articles slid into some big keyword terms, trending at the moment. Brought in thousands of visitors.
Typically however, you won't see a ton unless you're on a major site or 'breaking a story,' everyone catches onto... then begin linking to you as the source. I have done this as well. this is where the MAJOR traffic comes in. You have to really just know what you're doing with your target niche.
When I did this however, the website with the article had to upgrade their Godaddy account 4x, until they found a plan stable enough to hold the traffic. Article went viral on a social media group with like 2-million members..... FLOOD OF TRAFFIC... and a lot of big blogs pointed back to the news article. Created a high-power back link for the client's site and a ton of trickle down traffic.