Ads which appear below the fold will be cheaper than those above the fold due to the chance of not being viewed. For this reason, the content that is less likely to attract interest of majority of visitors is placed below the fold.
For example, technical specifications of the device that interest only limited amount of consumers may be relegated below the fold, while the fold itself is used to present more striking information. False bottom is the effect which makes visitors believe the web page ends below the fold and various techniques are used to attract visitors attention and induce them to scroll down. Mostly it is in the form of links to the content below or visual indicators that the content continues further down (pointers and arrows).