Play while streaming announced for Playstation 4

Sony has announced that their console will be able to play games as they are downloaded onto the console.

The details so far reveal this is done through new processors that also allow things to be downloaded while the console is off. The console will also download games that players may be interested in playing, before they even want or know about it. Some of the features are similar to how the PS Vita operates, but is much more powerful.

The systems new specs, that include 8GB of RAM and a backgroung specific processor, will allow the console to do some things that seem almost psychic. While this feature has an interesting future, how does it prevent a hard-drive filled up with unwanted data?