In an effort to further make downloading easier for its customers, Steam has announced the creation of their new content system designed to make downloading titles a more customized experience. The new system is meant to help give you more control such as bandwith throttling, prioritizing which games get downloaded first, scheduling downloads and also allowing more downloads when demand is high such as a new release. How it simplifies is by instead of updating a whole file for the game, the system will download only what you need for said file while new content will be updated for a game as you exit it.
[ Source: Steam ]