It is not necessary to register your device. There are 3 main reasons for registering a thermostat:
1. Remote access via CloudConnect. Annual service fees apply.
2. Remote access via DirectConnect. Router port forwarding is required. No annual fees.
3. Courtesy connectivity alerts. If a registered thermostat does not "phone home" in any 4-hour period, a courtesy email is sent to the log-in email address.