Assuming mobile data is $10/GB, a 1MB video ad costs the end user 1 cent. Quality (though not premuim) mobile ad space has a CPM of about $5, or a cost per impression of half a cent. So whenever you see an ad in a mobile app and you aren't on WiFi, you are paying 1 cent to use the app _and_ watch an ad and the publisher is getting less than half a cent (ad rev share) from the advertisers. The end user and the publisher would be better off if they just paid the publisher half a cent directly.