The primary reason to register your ECID with third-party services is to .
Apple uses this ID during the "signing" process. When you restore your device, iTunes (or Finder) sends your ECID to Apple’s servers. Apple then sends back a digital signature (SHSH2 blob) that allows the installation of iOS. Why Should You Register Your ECID?
Registering Your ECID: The Complete Guide to iPhone Saving & Restoration