Targeted advertising.
You may think it's useful, because you get relevant adverts.
You may think it's annoying.
The very clever algorithm looks for relevant words on the page, and places adverts which include relevant items alongside the articles.
Thus, when the Daily Telegraph's mobile website reported this story about the boy being killed on a skiing holiday, the Telegraph's err "clever" algorithm put an advert next to the article for ...
Specsavers!
The advert featured a boy skiing, and flying through the air, as his glasses fell off.
The advertising along was "Some things are better with contact lenses".