When you go to register if I remember it directs you here:
Its a simple process, no credit card or anything needed.
Its to register for your trial period of access, apps, 911 etc (like onstar), remote start phone app etc. You dont HAVE to register to use the radio/NAV/travel link and sat radio.
If you have the 8.4 NAV you get a year free trial, if not you get 6 months.
Most dealers know very little about it, I had to register mine myself.