We have run into issues when one deskphone in a ring group is unplugged for one reason or another and the ring group stops working correctly. The inbound call rings for maybe half a ring and then hangs up on the caller.
We have also run into issues when a user within a ring group forwards their deskphone to another deskphone. When this happens all calls to that ring group only rings the deskphone on the receiving end of the call forward.
Other phones systems that I have worked with have a complete separation of the ring group and the endpoints. This allows any issues that are happening with the endpoint to be ignored by the system maintaining continuity of the ring group at all times.