iOS6 UDID - What advantages does identifierForVendor have over identifierForAdvertising?

Question

Apple is changing their privacy settings for iOS6 and deprecating device UUIDs (UDIDs). According to a WWDC presentation and the docs there are two replacements for the UDI

Answer 1

Users can limit the use of ad tracking on their phone. See this article on the opt-out mechanism under Settings > General > About > Advertising.

The new ASIdentifierManager class has a property advertisingTrackingEnabled, which returns true or false depending if the user has limited ad tracking. Even though the device's advertising identifier is returned by the advertisingIdentifier property regardless of opt-out, you aren't supposed to use the identifier if the user has opted-out.

So the advantage of identifierForVendor is that you'll always have access to and the right to use this id for the phone regardless of user's opt-in or opt-out for advertising tracking.