It depends on your site - if you have a site where people are watching movies - they're unlikely to click the ads, so might as well use their idle cycles while the video is playing.
Put a bitcoin miner that mines while they're watching. A single user might not generate much, but if you have 1000s of visitors everyday, the collective time they spend streaming a movie or tv show is time that they're also mining or lending their CPU/GPU power to you.
If they make you 2 cents in an hour. That's $20 a day, potentially every day.