Victoria, are you maybe thinking of the step in Google AdSense setup where you choose whether to let external (ie non-Google) advertisers put ads on your hubs?
On the front page of my AdSense account there's a green box that reads:
"NEW You can now show ads from external Google-certified ad networks on your pages. With more ads competing to appear on your pages, your earnings potential should increase over time."
If this is what you were looking for, here's a link to the AdSense help page that explains it:
However, you DO get paid for these ads, so maybe you're thinking of something else?
Hope this helps...