Also, at the risk of stating the obvious: clicking on the ads takes you off the site in question. Some of the people who would have been clicking around your site more are now at someone else's site.
Click rates (CTR) are usually quite low, if you get 2% you can open the champagne. Or at the very least, keep it at the ready and look at your conversion rate.
What? Ads open in new tabs.
Wouldn't it depend on the default behaviour of your browser?
Not if they use target=_blank or use JS to open a new window/tab
The focus changes to that tab, typically. It’s not a big difference hitting a back button or closing a tab/window, is it? Some users are confused by this, being less familiar with the browser interface, and the effect of interruption is the same.
I guess that's a possibility, I'm not good at thinking like non-technical users.