If you're looking to become the next mayor of a virtual city, just make sure you have an internet connection. Otherwise, all of your hard work will go down the drain about as quickly as you can shut down your computer. That's right, the next SimCity will need a persistent Internet connection to play.
But, it's a bit more important than most games make it. Some require it to start, however SimCity will require it to save the game. This could prove troublesome if your Internet goes down while playing. Think about it--you might have to restart your system to get the connection back, but you can't do that because you can't save.
The reasoning behind the constant connection is both for piracy reasons, but also because of the multiplayer features, according to Maxis' Stone Librande. In response to a Reddit question, Maxis responded that if you lose your connection, you'll be allowed "to play for as long as we can preserve your game state," which is a period that will "likely be minutes."