Update: iOS 6 deprecated the purpose property and it now has to be set in your Info.plist with the key NSLocationUsageDescription which is displayed in Xcode as Privacy – Location Usage Description. If you’re still supporting iOS 5 and earlier make sure you include both.

A great, but underused location feature on iOS is the purpose property of the CLLocationManager.

So many apps ask for your location – give your users confidence in sharing their location by telling them why you need it!

Example:

locationManager.purpose = @"We'll only use your location to show you local events nearby.";

You need to do this before you start the location monitoring, so:

CLLocationManager *locationManager = [[CLLocationManager alloc] init];
locationManager.purpose = @"We'll only use your location to show you local events nearby.";
locationManager.delegate = self;
[locationManager startUpdatingLocation];

Your users will now get a pleasant reason when you request their permission:

I’ve no idea why this is so rarely used, it’s been available since iOS 3.2.

Tip from the Apple docs:

You must set the value of this property prior to starting any location services. Because the string is ultimately displayed to the user, you should always load it from a localized strings file.