If you're the owner of a 12GB PlayStation 3 and plan to continue playing Grand Theft Auto 5's GTA Online mode, you're going to need to purchase a bigger hard drive for more storage.
According to Rockstar, PS3 owners — specifically those with a 12GB hard drive — will need additional storage to accommodate future GTA 5 Title Updates after 1.16, which was released on August 19. The developer notes that "all updates and content must remain installed on the system in order to maintain compatibility for all players within GTA Online." If there's not enough space available on the system, the hardware limitations will prevent you from accessing GTA Online; however, GTA 5's Story Mode will still be playable without being connected to PSN, and without additional updates.
GTA Online players are still awaiting the arrival of Heists, but it's expected that Rockstar will continue to support GTA Online and continue adding new content well into the future — especially since the game's PC, Xbox One, and PS4 editions are to launch soon. Rockstar just released a pretty massive San Andreas Flight School update, adding a bunch of new missions and vehicles (including planes and helicopters).