When developing any software it’s important to make sure everything flows smoothly. This can be tougher when it comes to network connections as they’re unreliable, especially on a mobile device where the connection can drop out frequently or can be extremely slow (if you’re using 3G).
Aside from just chucking up an error message if there’s a problem, good usability starts before you ever make your network connection. Using Apple’s reachability class lets you easily see when your iOS device connects or disconnects from the net. You can also tell whether it’s Wifi you’re connected to or 3G, good for not downloading too much and eating up all the user’s cellular data.