Making ads sticky can help to improve viewability percentages – viewability is important to many advertisers.
Ads can be made to stick for a short period of time and then disappear, or they can be set up to be “perma-sticky” – so they don’t go away.
When ads are permanently stuck, publishers need to be careful that there’s sufficient space to display everything on the page.
Here’s what I saw on the Telegraph today, while viewing a story: