Different UUID from IDFA and IDFV

So I just read from the Leanplum’s document, that UUID can come from 2 sources, they are IDFA (advertisingIdentifier) and IDFV (identifierForVendor).

Basically, from what I read on https://gist.github.com/hujunfeng/6265995 (thanks hujunfeng!),

• UUID from IDFA (ASIdentifierManager.shared().advertisingIdentifier.uuidString) will remain same for all apps in a device. The value will only changed when user does full reset on the device, or manually reset the advertising idenfifier.
• UUID from IDFV (UIDevice.current.identifierForVendor?.uuidString) will be different for (almost) all apps in a device. I say "almost", because some apps that comes from "same prefix" of Bundle ID (e.g: com.calculator.apps, and com.calculator.apps2) will be have the same UUID IDFV. The value will changed when all of that "same prefix" Bundle ID apps are deleted / uninstalled and then reinstalled.

So that’s it. Now We know which the best for us for defining the “Device ID” of our users.