Haptics helps you signal important information in multiple modes. For example, you can use a UINotificationFeedbackGenerator to reinforce some "warning" feedback. Twitter uses this when you are running out of characters when composing a tweet.

Tweet composer screen. There are 20 remaining characters to reach the limit. Multiple modes are used to signal this information: Shape, with the circular progress indicator; Text, with the remaining characters left; Color, using yellow for the few characters left warning; and Haptic Feedback. For the latter, you can create a UINotificationFeedbackGenerator and call notificationOccured passing the .warning option.