Many mobile webpages, such as shown in this screen shot from Huffington Post, force the user to click on a button before displaying the whole article.
The clicking does not seem to improve the experience, nor is it intended to be used as a paywall to entice potential conversions.
It is unlikely to be for saving bandwidth, as many bandwidth intensive images load along with the button. It appears to me to be there solely as a source of annoyance.
Why, then, is this tactic so widely used?