These are used by Donky to create a virtual user on the network for you to send messages from and receive them to (much like an originator for SMS). An app identity is essentially a fictional user and device which allows you to exist on the network. There may be more than one App Identity in an App Space (e.g. customer service, personal shopper, complaints) and they can be used as IDs for data forwarding should you wish to set it up. You may also add app identities as Standard Contacts within your app to allow your users to send unsolicited inbound messages to you.