Along the same lines as the startup warning when starting as a standalone but local.system.replset contains documents. If a shardsvr starts and there are CWRWC defaults persisted, then they will not be used, and further indicate that the node had a former life as a configsvr or plain replset. Since those CWRWC defaults would have been used during the former life, but aren't now, the warning should alert the admin to this fact.