Because if you use your own shortener, then you can switch the storage without breaking the links. And using you own domain and service gives you control. Obvi

Because if you use your own shortener, then you can switch the storage without breaking the links. And using you own domain and service gives you control. Obviously this only works when you use your own personal URL-Shortener and not one of the ubiqious cost free shortening services like bit.ly et.al.