I don't have a proper business per se, but I do make a living from a puzzles (flash and javascript games) site with adsense.

I use the API to see what games are trending right now, and use that to order the games on various "listings". That way, new and cool stuff are always on top.

I can also see exactly what times most people get on the website, and I use that information to send newsletters(and posts social media) on what I think is the best time.

I see what games are more engaging and I can focus on them, writing more features or simply promoting them better.

At the end of day, you won't get much more data than from a traditional tool like Google Analytics. But the real-time nature and the presentation make your data so vibrant that you check Chartbeat 100 times a day—everytime you get some small hints and insights you would overlook without. Basically with Chartbeat your site lives and breaths.