Device Token requirement in push notification

I actually implemented push notification service into my game but I have some questions in my mind those I want to clear.

Implementation totally done on our custom server so not used any third party service help in this. I have used core Unity push notification code for this purpose.

http://docs.unity3d.com/ScriptReference/iOS.NotificationServices.RegisterForNotifications.html

After registration was complete, I need to add deviceToken to web server. Why I need to do...

Device Token requirement in push notification