Along with the introduction of drug dealing, every safehouse has a stash box in which the player can stash collected drugs to free up space in the holdall or prevent the drugs from being taken by the police when busted.
The whiteboard is used to replay previously completed story missions and to input cheats in the iPhone/iPod touch versions. The laptop is used to upload stats using Nintendo's Wi-Fi connection, viewable on the Rockstar Social Club. The couch is used to save the game to restore the player's health, remove wanted levels, and advance the game by six hours. The door is used to exit the safehouse. Rewards in the form of objects can be seen placed on shelves and on tables for the player to view.
In Grand Theft Auto IV, the safehouse area is just a parking lot, so it is possible that the apartment has not been constructed yet.